Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
Last revision Both sides next revision
sanboot:ubuntu_iscsi [2010/08/11 12:26]
cinquero
sanboot:ubuntu_iscsi [2010/08/16 20:51]
cinquero
Line 233: Line 233:
  
   * 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. Especially because SAN boot using gpxe seems to not allow using a MaxSessions=1/​MaxConnections=1 setting for the target, which would prevent concurrent accesses -- a very basic need for data integrity purposes.

QR Code
QR Code sanboot:ubuntu_iscsi (generated for current page)