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Vladislav Bolkhovitin
@@ -45,7 +45,7 @@
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<div id="main">
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<h1>Features comparison between Linux SCSI targets</h1>
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<p><small>As on October 2009</small></p>
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<p><small>As on October 2009. Partially updated in August 2010.</small></p>
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<table bgcolor="#F0F0F0" border="1" cellspacing="1" cellpadding="7" style="text-align:center" width="620">
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@@ -64,7 +64,7 @@
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<td align="left"><b>Upstream kernel</b></td> <td> - </td> <td> Kernel part </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Generic Target Engine</b></td> <td> + </td> <td> + </td> <td> iSCSI only </td> <td> Under development </td>
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<td align="left"><b>Generic Target Engine</b></td> <td> + </td> <td> + </td> <td> iSCSI only </td> <td> + </td>
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</tr>
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<tr>
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<td align="left"><b>Architecture</b></td> <td> Kernel only</td> <td> User space only
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@@ -74,7 +74,7 @@
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<tr>
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<td align="left"><b>Stability</b></td> <td> + </td> <td> +
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<sup><A HREF="#3">3</A>
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</sup> </td> <td> + </td> <td> Under development </td>
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</sup> </td> <td> + </td> <td> ? (no released packages) </td>
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</tr>
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<tr>
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<td align="left"><b>Performance <sup><A HREF="#4">4</A></sup></b></td> <td> ***** <sup>
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@@ -95,7 +95,7 @@ backend drivers</th> <td> + <sup>
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transfer values (parallel SCSI, SAS)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Interface with user space</b></td> <td> ProcFS </td> <td> Custom </td> <td> - </td> <td> ConfigFS/IOCTL/ProcFS </td>
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<td align="left"><b>Interface with user space</b></td> <td> SysFS/ProcFS </td> <td> Custom </td> <td> - </td> <td> ConfigFS/IOCTL/ProcFS </td>
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</tr>
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@@ -103,7 +103,7 @@ transfer values (parallel SCSI, SAS)</b></td> <td> + </td> <td> - </td> <td
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<td colspan="5"><b>Major features</b>
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</td></tr>
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<tr>
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<td align="left"><b>Target drivers in kernel space</b></td> <td> + </td> <td> + </td> <td> - </td> <td> Under development </td>
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<td align="left"><b>Target drivers in kernel space</b></td> <td> + </td> <td> + </td> <td> - </td> <td> + </td>
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</tr>
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<tr>
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<td align="left"><b>Target drivers in user space</b></td> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
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@@ -112,15 +112,11 @@ transfer values (parallel SCSI, SAS)</b></td> <td> + </td> <td> - </td> <td
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<td align="left"><b>Backstorage handlers in kernel space</b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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</tr>
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<tr>
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<td align="left"><b>Backstorage handlers in user space</b></td> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
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<td align="left"><b>Backstorage handlers in user space</b></td> <td> + </td> <td> + </td> <td> - </td> <td> Through STGT </td>
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</tr>
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<tr>
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<td align="left"><b>Local access to emulated backstorage devices
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<sup><A HREF="#9">9</A></sup></b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Advanced devices access control
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<sup><A HREF="#10">10</A></sup></b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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<sup><A HREF="#10">10</A></sup></b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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</tr>
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<tr>
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<td align="left"><b>Support for Asynchronous Event Notifications
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@@ -132,14 +128,10 @@ resized through AENs or Unit Attentions (Initiators can instantly see
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any target reconfiguration in a PnP-like fashion)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Bidirectional Commands</b></td> <td> + <sup>
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<A HREF="#11">11</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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<td align="left"><b>Bidirectional Commands</b></td> <td> +</td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Extended CDB (size >16 bytes)</b></td> <td> + <sup>
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<A HREF="#11">11</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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<td align="left"><b>Extended CDB (size >16 bytes)</b></td> <td> +</td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Descriptor sense support</b></td> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
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@@ -169,8 +161,7 @@ ORDERED commands</b></td> <td> + </td> <td> + </td> <td> -, <br> data
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</tr>
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<tr>
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<td align="left"><b>Persistent Reservations <br>
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<small> (Windows 2008 clustering / RHEL5 I/O fencing)</small></b></td> <td> Under testing
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</td> <td> + <br> (limited
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<small> (Windows 2008 clustering / RHEL5 I/O fencing)</small></b></td> <td> + </td> <td> + <br> (limited
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functionality
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implemented)</td> <td> - </td> <td> + </td>
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</tr>
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@@ -181,6 +172,19 @@ ORDERED commands</b></td> <td> + </td> <td> + </td> <td> -, <br> data
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<td align="left"><b>Failover Clustering</b></td> <td> + </td> <td> ? </td> <td> + </td> <td> + </td>
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</tr>
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<tr>
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<td align="left"><b>Allocated buffers cache</b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Protection against commands with
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wrong transfer size or transfer direction (may lead to crash or
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hard lockup)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Protection against DoS'ing target by making it
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allocate too much memory for buffers and taking it into an OOM state
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</b></td> <td> + </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>SCSI MIBs</b></td> <td> - </td> <td> - </td> <td> - </td> <td> +-
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<sup><A HREF="#15">15</A></sup></td>
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</tr>
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@@ -213,9 +217,8 @@ ORDERED commands</b></td> <td> + </td> <td> + </td> <td> -, <br> data
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<td align="left"><b>Marvell (SAS)</b></td> <td> Beta </td> <td> - </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>FCoE</b></td> <td> Under
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development </td> <td>Under
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development</td> <td> - </td> <td> - </td>
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<td align="left"><b>FCoE</b></td> <td> Alpha </td> <td>Under
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development</td> <td> - </td> <td> Alpha </td>
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</tr>
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<tr>
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<td align="left"><b>LSI (Parallel (Wide) SCSI and Fibre Channel)
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@@ -227,7 +230,11 @@ ORDERED commands</b></td> <td> + </td> <td> + </td> <td> -, <br> data
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</tr>
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<tr>
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<td align="left"><b>IBM pSeries Virtual SCSI</b></td> <td> - </td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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</tr>
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<tr>
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<td align="left"><b>Local access to emulated backstorage devices
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<sup><A HREF="#9">9</A></sup></b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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</tr>
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<tr bgcolor="#E0E0E0">
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<td colspan="5"> <b>Supported backstorage</b>
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@@ -243,11 +250,13 @@ ORDERED commands</b></td> <td> + </td> <td> + </td> <td> -, <br> data
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</tr>
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<tr>
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<td align="left"><b>SCSI pass-through
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<sup><A HREF="#16">16</A></sup></b></td> <td> + </td> <td> Disks only, single
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<sup><A HREF="#16">16</A></sup></b></td> <td> + </td> <td> Single
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initiator only, not
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enforced <sup>
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enforced, limited
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for tapes <sup>
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<A HREF="#17">17</A>
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</sup> </td> <td> - </td> <td> Single initiator only, not enforced
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</sup> </td> <td> - </td> <td> Single initiator only, not enforced,
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limited for tapes
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<sup><A HREF="#17">17</A></sup></td>
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</tr>
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<tr>
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@@ -293,14 +302,15 @@ devices (VTL)</b></td> <td> - </td> <td>Experimental</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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<td align="left"><b>Interface with user space</b></td> <td>IOCTL/ProcFS/
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<td align="left"><b>Interface with user space</b></td> <td>SysFS/IOCTL/ProcFS/
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Netlink</td> <td> - </td> <td>IOCTL/ProcFS/
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Netlink</td> <td> ConfigFS/IOCTL/ProcFS </td>
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</tr>
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<tr>
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<td align="left"><b>Zero-copy data send/receive</b></td> <td> Send only<sup>
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<A HREF="#19">19</A>
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</sup> </td> <td> None <sup>
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</sup> </td> <td> In some cases,
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send only <sup>
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<A HREF="#8">8</A>
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</sup> </td> <td> Send only</td> <td> Send only </td>
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</tr>
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@@ -312,14 +322,10 @@ devices (VTL)</b></td> <td> - </td> <td>Experimental</td> <td> - </td> <
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<td align="left"><b>Max ErrorRecoveryLevel</b></td> <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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<td align="left"><b>Bidirectional Commands</b></td> <td> + <sup>
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<A HREF="#11">11</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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<td align="left"><b>Bidirectional Commands</b></td> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Extended CDB (size >16 bytes)</b></td> <td> + <sup>
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<A HREF="#11">11</A>
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</sup></td> <td> + </td> <td> - </td> <td> - </td>
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<td align="left"><b>Extended CDB (size >16 bytes)</b></td> <td> + </td> <td> + </td> <td> - </td> <td> - </td>
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</tr>
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<tr>
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<td align="left"><b>Support for Asynchronous Event Notifications
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@@ -336,7 +342,7 @@ reinstatement <sup><A HREF="#20">20</A></sup></b></td> <td> Safe </td> <td> N
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<tr>
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<td align="left"><b>Support for <a href="max_outstanding_r2t.txt">
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MaxOutstandingR2T >1</a> (write performance increase on high latency
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links)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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links)</b></td> <td> + </td> <td> Partial </td> <td> - </td> <td> + </td>
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</tr>
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<tr>
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<td align="left"><b>iSCSI MIBs</b></td> <td> - </td> <td> - </td> <td> - </td> <td> +-
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@@ -374,7 +380,8 @@ links)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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<p><A NAME="8"></A> 8. Some zero-copy functionality isn't available from user space, sometimes fundamentally.
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For instance, zero-copy FILEIO with page cache or zero-copy send to a socket. Also STGT can't use splice() for in-kernel
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target drivers, because it has memory management in user space. To use splice() with socket-based user space target drivers
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STGT would need a deep redesign of internal interactions between target drivers, core and backend handlers.</p>
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STGT would need a deep redesign of internal interactions between target drivers, core and backend handlers. But in
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some cases STGT can use zero-copy sendfile().</p>
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<p><A NAME="9"></A> 9. 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 from emulated by the target
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@@ -384,8 +391,6 @@ links)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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of devices from the same target. This feature is required for hardware targets, which don't have ability
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to create virtual targets.</p>
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<p><A NAME="11"></A> 11. Not well tested, because at the moment there is no backend using this functionality.</p>
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<p><A NAME="12"></A> 12. 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. This is what was called
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@@ -414,11 +419,14 @@ links)</b></td> <td> + </td> <td> - </td> <td> - </td> <td> + </td>
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SCSI tape or SATA DVD-RW device to your iSCSI network.</p>
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<p><A NAME="17"></A> 17. STGT and LIO don't emulate all the necessary SCSI host functionality to allow to share SCSI devices
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in pass-through mode to several initiators. They can only pass SCSI commands from initiators to
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in pass-through mode to several initiators, although LIO has some necessary processing, but not all.
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They can only pass SCSI commands from initiators to
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SCSI devices and responses back. This is safe only with a single initiator. This limitation
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isn't enforced anyhow and both STGT and LIO don't issue any warning about it, so an user will not be notified about this
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limitation and can quietly corrupt his/her data. You can find more technical information about it
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<a href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">here</a>.</p>
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<a href="http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg06911.html">here</a>.
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Also neither STGT, nor LIO in pass-through mode do the necessary sense processing for tape devices to
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correctly return residual information, so tapes can used with them with limited functionality.</p>
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<p><A NAME="18"></A> 18. You can find a proposal how to implement zero-copy FILEIO in SCST on the <a href="contributing.html#ZC_READ">
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Contributing</a> page.</p>
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@@ -113,7 +113,8 @@
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iscsi-scstd.conf file in /etc, but using corresponding SCST facilities. This is because now responsibilities
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are divided (as it logically should be) between the target driver (iSCSI-SCST) and the SCSI target core (SCST),
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where target driver is responsible for handling targets with their parameters, and SCST core is responsible for handling
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backstorage.</p>
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backstorage. You can also use a migration tool developed by Scalable Informatics Inc., which will convert your IET machine
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to an iSCSI-SCST machine. See README for more details.</p>
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<p>The latest stable version is 1.0.1.1. Requires Linux kernel version 2.6.16.x or higher and SCST version 1.0.1.1 or higher.
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Tested mostly on i386 and x86_64, but should work on any other supported by Linux platform.</p>
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