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sanboot:ubuntu_iscsi [2010/08/11 12:26]
cinquero
sanboot:ubuntu_iscsi [2010/08/16 20:50]
cinquero
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   * Enable data journaling. That will cut your maximum write performance in half.   * Enable data journaling. That will cut your maximum write performance in half.
-  * Increase ​node.session.timeo.replacement_timeout in iscsid.conf to avoid escalation of temporary connection problems to upper layers. In *my* situation it *never* makes sense to tell the ext4 driver about I/O problems because there is no fallback. It would just give me a corrupted ​filesystem.+  * One may increase ​node.session.timeo.replacement_timeout in iscsid.conf to avoid escalation of temporary connection problems to upper layers. In *my* situation it (almost) ​*never* makes sense to tell the ext4 driver about I/O problems because there is no fallback. It would just give me an unclean filesystem (not unmounted properly, like hard reset). However(!!),​ an unclean ​filesystem ​may be better than a totally screwed one: imagine your iSCSI target host crashes, looses some data that still has not been written to disk, and the client continues to use that target without doing a journal replay first... personally, I try to avoid that situation by never starting the iSCSI target automatically (removed from init scripts, starting it manually after killing the client machines...). IMHO the iSCSI protocol is a bit dumb. The target should detect a crash and refuse session continuation after restart... again, I'm not liable for *any* sort of data loss if you act according to these explanations. You *will* screw your data. Sooner or later.

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