mirror of
https://github.com/SCST-project/scst.git
synced 2026-08-19 05:36:22 +00:00
Vladislav Bolkhovitin
e6a57baa14
git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@162 d57e44dd-8a1f-0410-8b47-8ef2f437770f
116 lines
4.2 KiB
Plaintext
116 lines
4.2 KiB
Plaintext
iSCSI SCST target driver
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========================
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Version 0.9.6/XXXX, XX XXX 200X
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-------------------------------
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This driver is a forked with all respects version of iSCSI Enterprise
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Target (IET) (http://iscsitarget.sourceforge.net/) with updates to work
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over SCST as well as with many improvements and bugfixes (see ChangeLog
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file). The reason of fork is that the necessary changes are intrusive
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and with the current IET merge policy, where only simple bugfix-like
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patches, which doesn't touch the core code, could be merged, it is very
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unlikely that they will be merged in the main IET trunk.
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To let it be installed and work at the same host together with IET
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simultaneously all the driver's modules and files were renamed:
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* ietd.conf -> iscsi-scstd.conf
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* ietadm -> iscsi-scst-adm
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* ietd -> iscsi-scstd
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* iscsi-target -> iscsi-scst
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* iscsi-target.ko -> iscsi-scst.ko
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This version is compatible with SCST version 0.9.6 and higher.
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Tested on 2.6.21.1 kernel, but it should also work on other versions,
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starting from 2.6.16.x.
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Installation
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------------
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Basically as in README-IET, where file names are changed as specified
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above.
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To use full power of TCP zero-copy transmit functions, especially
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dealing with user space supplied via scst_user module memory, iSCSI-SCST
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needs to be notified when Linux networking finished data transmission.
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Patch put_page_callback.patch provides such functionality. The
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corresponding version of it should be applied on your kernel. This is
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highly recommended, but not required. If it isn't applied, iSCSI-SCST
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will work in the performance degraded mode, when for data transmission:
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- For in-kernel allocated memory (scst_vdisk and pass-through
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handlers) usage of SGV cache on transmit path (READ-type commands)
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will be disabled. The performance hit will be not big, performance
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will still remain better, than for IET, because SGV cache will remain
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used on receive path and IET doesn't have such feature.
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- For user space allocated memory (scst_user handler) all transmitted
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data will be additionally copied into temporary TCP buffers. The
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performance hit will be quite noticiable.
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If you need your own version of put_page_callback.patch for your custom
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kernel, for which there is no prepared version, you can create it
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yourself. For that it is only necessary:
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1. Apply the closest version of put_page_callback.patch on your kernel.
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Resolve only failed hanks from include/ and net/core/utils.c, ignore
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other failures.
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2. Grep net/ and replace everywhere, except in net/sunrpc/svc.c and
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net/core/pktgen.c, put_page() by net_put_page() and get_page() by
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net_get_page().
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That's all.
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Usage
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-----
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ISCSI parameters like iSNS, CHAP and target parameters are configured in
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iscsi-scstd.conf. All LUN information is configured using the regular
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SCST interface. The LUN information in iscsi-scstd.conf will be ignored.
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This is because now responsibilities are divided (as it should be)
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between the target driver (iSCSI-SCST) and the SCST core. The target
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driver is responsible for handling targets and their parameters, SCST
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core is responsible for handling backstorage.
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If you need to configure different LUs for different targets you should
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create for each target group "Default_target_name", where target name
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means name of the target, for example:
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"Default_iqn.2007-05.com.example:storage.disk1.sys1.xyz", and add there
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all necessary LUNs. Check SCST README file for details.
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Compilation options
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-------------------
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There are the following compilation options, that could be commented
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in/out in the kernel's module Makefile:
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- DEBUG - turns on some debugging code, including some logging. Makes
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the driver considerably bigger and slower, producing large amount of
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log data.
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- TRACING - turns on ability to log events. Makes the driver considerably
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bigger and lead to some performance loss.
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- EXTRACHECKS - adds extra validity checks in the various places.
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- DEBUG_DIGEST_FAILURES - simulates digest failures in random places.
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Credits
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-------
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Thanks to:
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* IET developers for IET
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* Ming Zhang <blackmagic02881@gmail.com> for fixes
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* Krzysztof Blaszkowski <kb@sysmikro.com.pl> for many fixes
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* Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> for comments and help in
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debugging
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Vladislav Bolkhovitin <vst@vlnb.net>, http://scst.sourceforge.net
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