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Comparison page updates
git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@754 d57e44dd-8a1f-0410-8b47-8ef2f437770f
This commit is contained in:
Vladislav Bolkhovitin
+62
-52
@@ -71,15 +71,19 @@
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</sup> </td> <td> Kernel only </td>
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</tr>
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<tr>
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<th align="left"> Stability </th> <td> + </td> <td> + </td> <td> + </td> <td> Heavy development </td>
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<th align="left"> Stability </th> <td> + </td> <td> +
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<sup><A HREF="#3">3</A>
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</sup> </td> <td> + </td> <td> Heavy development </td>
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</tr>
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<tr>
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<th align="left"> Performance </th> <td> ***** </td> <td> ***</td> <td> **** </td> <td> ****
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<sup><A HREF="#3">3</A></sup></td>
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<th align="left"> Performance <sup><A HREF="#4">4</A></sup></th> <td> ***** <sup>
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<A HREF="#5">5</A>
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</sup></td> <td> ***</td> <td> **** </td> <td> ****
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<sup><A HREF="#6">6</A></sup></td>
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</tr>
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<tr>
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<th align="left"> Zero-Copy </th> <td> **** </td> <td> ***
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<sup><A HREF="#4">4</A>
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<sup><A HREF="#7">7</A>
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</sup> </td> <td> **** </td> <td> **** </td>
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</tr>
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<tr>
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@@ -87,7 +91,7 @@
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transfer values (parallel SCSI, SAS) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<th align="left"> User Interface </th> <td> ProcFS </td> <td> Custom </td> <td> IOCTL/ProcFS </td> <td> ConfigFS/IOCTL </td>
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<th align="left"> User Interface </th> <td> ProcFS </td> <td> Custom </td> <td> IOCTL/ProcFS </td> <td> ConfigFS/IOCTL/ProcFS </td>
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</tr>
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@@ -107,10 +111,12 @@ transfer values (parallel SCSI, SAS) </th> <td> + </td> <td> - </td> <td> -
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<th align="left"> Backstorage handlers in user space </th> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<th align="left"> Local access to emulated backstorage devices</th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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<th align="left"> Local access to emulated backstorage devices
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<sup><A HREF="#8">8</A></sup></th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<th align="left"> Advanced devices visibility management </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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<th align="left"> Advanced devices visibility management
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<sup><A HREF="#9">9</A></sup></th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<th align="left"> Support for Asynchronous Event Notifications
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@@ -124,12 +130,12 @@ transfer values (parallel SCSI, SAS) </th> <td> + </td> <td> - </td> <td> -
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</tr>
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<tr>
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<th align="left"> Bidirectional Commands </th> <td> + <sup>
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<A HREF="#5">5</A>
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<A HREF="#10">10</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<th align="left"> Extended CDB (size >16 bytes) </th> <td> + <sup>
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<A HREF="#5">5</A>
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<A HREF="#10">10</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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@@ -139,10 +145,10 @@ transfer values (parallel SCSI, SAS) </th> <td> + </td> <td> - </td> <td> -
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<small> (Windows 2003 clustering) </small></th> <td> + </td> <td> + </td> <td> + </td> <td> + </td>
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</tr>
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<th align="left"> Safe RESERVE/RELEASE implementation according to
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SCSI requirements <sup><A HREF="#6">6</A></sup></th> <td> Safe </td> <td> Safe </td> <td> Not safe </td> <td> Not safe </td>
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SCSI requirements <sup><A HREF="#11">11</A></sup></th> <td> Safe </td> <td> Safe </td> <td> Not safe </td> <td> Not safe </td>
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</tr>
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<th align="left"> Safe implementation of Task Management commands
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<sup><A HREF="#7">7</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
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<sup><A HREF="#12">12</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
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</tr>
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<tr>
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<th align="left"> Persistent Reservations <br/>
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@@ -155,7 +161,8 @@ SCSI requirements <sup><A HREF="#6">6</A></sup></th> <td> Safe </td> <td> Saf
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<th align="left"> Failover Clustering </th> <td> + </td> <td> ? </td> <td> + </td> <td> + </td>
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</tr>
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<tr>
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<th align="left"> SCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> + </td>
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<th align="left"> SCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> -
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<sup><A HREF="#13">13</A></sup></td>
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</tr>
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<tr>
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<th align="left"> Cluster Storage Integration </th> <td> - </td> <td> - </td> <td> - </td> <td> VHACS </td>
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@@ -207,7 +214,7 @@ SCSI requirements <sup><A HREF="#6">6</A></sup></th> <td> Safe </td> <td> Saf
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</tr>
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<tr>
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<th align="left"> SCSI Pass-through </th> <td> + </td> <td> - </td> <td> - </td> <td> Single initiator only, not enforced
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<sup><A HREF="#8">8</A></sup></td>
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<sup><A HREF="#14">14</A></sup></td>
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</tr>
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<tr>
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<th align="left"> 4k sectors support in pass-through mode </th> <td> + </td> <td> - </td> <td> - </td> <td> ? </td>
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@@ -232,19 +239,19 @@ in modes, other than pass-through </th> <td> + </td> <td> - </td> <td> - <
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</sup></td> <td> Kernel only </td>
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</tr>
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<tr>
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<th align="left"> MC/S </th> <td> - </td> <td> - </td> <td> - </td> <td> + </td>
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<th align="left"> Multiple connections per session (MS/C) </th> <td> - </td> <td> - </td> <td> - </td> <td> + </td>
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</tr>
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<tr>
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<th align="left"> Max ErrorRecoveryLevel </th> <td> 0 </td> <td> 0 </td> <td> 0 </td> <td> 2 </td>
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</tr>
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<tr>
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<th align="left"> Bidirectional Commands </th> <td> + <sup>
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<A HREF="#5">5</A>
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<A HREF="#10">10</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<th align="left"> Extended CDB (size >16 bytes) </th> <td> + <sup>
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<A HREF="#5">5</A>
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<A HREF="#10">10</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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@@ -252,33 +259,56 @@ in modes, other than pass-through </th> <td> + </td> <td> - </td> <td> - <
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(AEN) </th> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<th align="left"> Safe implementation of connections and sessions
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reinstatement <sup><A HREF="#9">9</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
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reinstatement <sup><A HREF="#15">15</A></sup></th> <td> Safe </td> <td> Not safe </td> <td> Not safe </td> <td> Not safe </td>
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</tr>
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<tr>
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<th align="left"> iSCSI MIBs </th> <td> - </td> <td> - </td> <td> - </td> <td> -
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<sup><A HREF="#10">10</A></sup></td>
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<sup><A HREF="#13">13</A></sup></td>
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</tr>
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</table>
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<br/>
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<p><strong><big><u>REMARKS:</u></big></strong></p>
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<p><A NAME="1"></A> 1. STGT has SCSI target engine in user space and small hooks in the kernel to interact with in-kernel target drivers.</p>
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<p><A NAME="1"></A> 1. STGT has SCSI target engine with memory management in user space and small hooks in the kernel to interact with in-kernel target drivers.</p>
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<p><A NAME="2"></A> 2. All iSCSI management implemented in user space and actual data transfers in kernel space without user space involved.</p>
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<p><A NAME="3"></A> 3. The conclusion made by source code study only. LIO should have performance
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on the IET level or slightly less, because of more processing overhead. </p>
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<p><A NAME="3"></A> 3. ISER target driver has long known (since Feb 2008) data corruption problem, which localization hasn't been determined yet and might be
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in the STGT core. See <a href="http://lists.berlios.de/pipermail/stgt-devel/2008-February/001367.html">
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http://lists.berlios.de/pipermail/stgt-devel/2008-February/001367.html</a> and
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<a href="http://lists.wpkg.org/pipermail/stgt/2009-February/002630.html">http://lists.wpkg.org/pipermail/stgt/2009-February/002630.html</a></p>
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<p><A NAME="4"></A> 4. Some zero-copy functionality isn't available from user space. For instance, zero-copy send to a socket.</p>
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<p><A NAME="4"></A> 4. The result "in average" is listed. One target can be better somewhere, another one somewhere else. Although manual tuning of target and
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system parameters tends the restore the difference listed in the comparison.</p>
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<p><A NAME="5"></A> 5. Not well tested, because at the moment there is no backend using this functionality.</p>
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<p><A NAME="5"></A> 5. All SCST and its drivers' kernel patches supposed to be applied and SCST with the drivers built in the release or performance build.
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Without the kernel patches SCST performance will be at "****+" level, except for the case, when user space backstorage handler used
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with iSCSI-SCST iSCSI target driver, where performance will be at "***+" level.</p>
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<p><A NAME="6"></A> 6. SCSI requires that if an initiator clears reservation held by another initiator, the reservation holder must be notified
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<p><A NAME="6"></A> 6. There is no performance data for LIO, which allow to make a direct comparison of it with other targets.
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The conclusion was made by source code study only. LIO should have performance on the IET level or less,
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because of more processing overhead. It might be much less for small block sizes.</p>
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<p><A NAME="7"></A> 7. Some zero-copy functionality isn't available from user space. For instance, zero-copy send to a socket.</p>
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<p><A NAME="8"></A> 8. "Local access to emulated backstorage devices" means that you can access emulated by a SCSI target devices
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locally on the target host. For instance, you can mount your ISO image as a SCSI CDROM device locally on the
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target host.</p>
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<p><A NAME="9"></A> 9. "Advanced devices visibility management" means that different initiators can see different sets
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of devices from the same target. This feature is essential with hardware targets, which don't have a possibility
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to create virtual targets.</p>
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<p><A NAME="10"></A> 10. Not well tested, because at the moment there is no backend using this functionality.</p>
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<p><A NAME="11"></A> 11. SCSI requires that if an initiator clears reservation held by another initiator, the reservation holder must be notified
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about the reservation clearance. Otherwise, several initiators can at the same time change supposed to be protected by the
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reservation data, which can corrupt them.</p>
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reservation data, which can corrupt them. This is what was called
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<a href="http://communities.vmware.com/thread/53797?tstart=0&start=15">"Russian roulette with your data"</a> by someone
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working for VMware on the VMware community forum.</p>
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<p><A NAME="7"></A> 7. After a task management command completed and corresponding response was sent to initiator, who sent that task management
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<p><A NAME="12"></A> 12. After a task management command completed and before the corresponding response was sent to the initiator, who sent that task management
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command, all the affected SCSI commands must get into a state, where they can't affect following after
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the tasks management response commands from this initiator. This is the safe implementation.
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The unsafe implementation only marks all the affected
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@@ -288,44 +318,24 @@ reinstatement <sup><A HREF="#9">9</A></sup></th> <td> Safe </td> <td> Not saf
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SCSI command, which initiator will send after it received the task management response thinking
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that all the aborted commands actually fully aborted. This could lead to a data corruption.</p>
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<p><A NAME="8"></A> 8. LIO doesn't emulate all the necessary SCSI host functionality to allow to share a SCSI device
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<p><A NAME="13"></A> 13. The IETF SCSI-MIB (RFC 4455) is not supported by LIO, only proprietary MIBs SBE-SCSI-MIB, SBE-ISCSI-MIB and SBE-IPS-AUTH-MIB are supported.
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<p><A NAME="14"></A> 14. LIO doesn't emulate all the necessary SCSI host functionality to allow to share a SCSI device
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in pass-through mode to several initiators. It can only pass SCSI commands from initiator to
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the SCSI device. This is safe only if there is only one initiator. This limitation
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isn't enforced anyhow by LIO. You can find more technical information about that in
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<a href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">
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http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html</a></p>
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<p><A NAME="5"></A> 9. Connections and sessions reinstatement is, basically, a kind of Task Management command.
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For instance, open-iscsi uses it as such in eh_target_reset_handler() callback. So, similarly
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<p><A NAME="15"></A> 15. Connections and sessions reinstatement is, basically, a kind of Task Management command, because it implies commands aborting.
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For instance, open-iscsi uses it as a less intrusive substistute for target reset in eh_target_reset_handler() callback. So, similarly
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to <A HREF="#7">(7)</A> above, a safe implementation
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must not accept SCSI commands from new connection/session until all the SCSI commands in
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being reinstated connection/session get into a state, where they can't affect the new commands.</p>
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<p><A NAME="10"></A> 10. SCSI-MIB (RFC 4455) - not supported;
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SBE-SCSI-MIB - supported by LIO v2.6, not supported by LIO v3.0;
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SBE-ISCSI-MIB - supported by LIO v2.6, not supported by LIO v3.0;
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SBE-IPS-AUTH-MIB - supported by LIO v2.6, not supported by LIO v3.0
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</p>
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<br/>
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<hr style="width: 100%; height: 1px; margin-left: 15px; margin-right: 0px;">
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<br/>
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<p><strong>P.S.</strong> LIO has similar comparison
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<a href="http://www.linux-iscsi.org/index.php/Overview_Page">page</a>. It is very much
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wrong about SCST. I asked that page author, Nicholas Bellinger, to
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correct the wrong items (see <a href="http://sourceforge.net/mailarchive/forum.php?thread_name=49AECE0B.5030009%40vlnb.net&forum_name=scst-devel">my e-mail</a>),
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but Nicholas Bellinger refused to do it. Moreover, he blocked my access
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to the LIO mailing list, preventing me from tell that to the interested
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people myself. After all our previous discussions and with his skills
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and experience I can't believe that Nicholas Bellinger doesn't know that
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SCST is a lot more generic than LIO and has zero-copy in all the same
|
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places, where LIO has. So, that comparison page looks like rather a
|
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deliberate cheating attempt. Definitely, SCST in all major
|
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technical areas is so much superior over LIO, so Nicholas Bellinger started
|
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attacking people's perception about SCST trying to inspire them the
|
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opposite.</strong></p>
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<p><small><strong>P.S.</strong> You can find a brief background history of this comparison page <a href="comparison_history.html">here</a>.</small></p>
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</div>
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</div>
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@@ -0,0 +1,73 @@
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta name="Keywords" content="Generic SCSI Target Middle Level for Linux" />
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
|
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<meta name="author" content="Daniel Fernandes"/>
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<meta name="Robots" content="index,follow" />
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<link rel="stylesheet" href="images/Orange.css" type="text/css" />
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<title>SCST: Generic SCSI Target Middle Level for Linux</title>
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</head>
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<body>
|
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<!-- wrap starts here -->
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<div id="wrap">
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<div id="header">
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<div class="logoimg"></div><h1 id="logo"><span class="orange"></span></h1>
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<h2 id="slogan">SCSI Target Middle Level for Linux</h2>
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</div>
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|
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<div id="menu">
|
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<ul>
|
||||
<li id="sponsorship"><a href="sponsorship.html">Sponsorship</a></li>
|
||||
<li><a href="index.html">Home</a></li>
|
||||
<li><a href="http://www.sourceforge.net/projects/scst">Main</a></li>
|
||||
<li><a href="targets.html">Drivers</a></li>
|
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<li><a href="downloads.html">Downloads</a></li>
|
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<li><a href="contributing.html">Contributing</a></li>
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<li id="current"><a href="comparison.html">Comparison</a></li>
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</ul>
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|
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<!-- content-wrap starts here -->
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<div id="content-wrap">
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<div id="sidebar">
|
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<h1>Target Drivers</h1>
|
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<ul class="sidemenu">
|
||||
<li><a href="comparison.html">Features comparison</a></li>
|
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<li><a href="scstvsstgt.html">SCST vs STGT</a></li>
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</ul>
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</div>
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<div id="main">
|
||||
|
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<h3>Some background history of the <a href="comparison.html">Features comparison</a> page.</h3>
|
||||
|
||||
<p>LIO was the first who has had similar comparison page
|
||||
http://www.linux-iscsi.org/index.php/Overview_Page. It was and still is very much
|
||||
wrong about SCST. I asked that page author, Nicholas Bellinger, to
|
||||
correct the wrong items (see <a href="http://sourceforge.net/mailarchive/forum.php?thread_name=49AECE0B.5030009%40vlnb.net&forum_name=scst-devel">my
|
||||
e-mail</a>), but Nicholas Bellinger refused to do it without any explanations. Moreover, he
|
||||
blocked my access to the LIO mailing list, preventing me from tell that
|
||||
to the interested people myself. After all our previous discussions and
|
||||
with his skills and experience it's nearly impossible to believe that Nicholas Bellinger
|
||||
didn't know that SCST is a lot more generic than LIO and has zero-copy
|
||||
in all the same places, where LIO has. So, that comparison page looked
|
||||
like rather a deliberate cheating attempt and for SCST there was no other way, except to setup own, correct comparison.
|
||||
This comparison table turned out to be very useful, so it was extended to cover all the SCSI target areas.</p>
|
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|
||||
</div>
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||||
</div>
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||||
</div>
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||||
<!-- wrap ends here -->␍
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||||
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|
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<div id="footer">
|
||||
<p>
|
||||
© Copyright 2008 <b><font color="#EC981F">Vladislav Bolkhovitin & others.</font>
|
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Design by: <b><font color="#EC981F">Daniel Fernandes</font></b>
|
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|
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|
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|
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<!-- footer ends here -->
|
||||
</body>
|
||||
</html>
|
||||
Reference in New Issue
Block a user