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sanboot:ubuntu_iscsi [2010/08/11 12:17]
cinquero
sanboot:ubuntu_iscsi [2010/08/16 20:55]
cinquero
Line 213: Line 213:
 find /etc -name '​S*open-iscsi'​ find /etc -name '​S*open-iscsi'​
 </​code>​ </​code>​
 +  * One possibly has to repeat the previous step when upgrading/​reinstalling open-iscsi.
   * create /​etc/​init/​open-iscsi.conf:​   * create /​etc/​init/​open-iscsi.conf:​
-<pre>+<code>
 description "​Open-iSCSI"​ description "​Open-iSCSI"​
  
 start on filesystem start on filesystem
 +# no stopping!
 exec /​etc/​init.d/​open-iscsi start exec /​etc/​init.d/​open-iscsi start
-</pre>+</code>
   * Lucid detects on its own if rootfs is an iscsi target. It will prevent network shutdown on shutdown and read-only remounting of the rootfs should make sure that data gets flushed to disk.   * Lucid detects on its own if rootfs is an iscsi target. It will prevent network shutdown on shutdown and read-only remounting of the rootfs should make sure that data gets flushed to disk.
 +  * For your own convenience,​ edit the following line in /​etc/​default/​grub as shown below:
 +<​code>​
 +GRUB_CMDLINE_LINUX_DEFAULT="​ip=dhcp ISCSI_INITIATOR=<​yourInitiatorName>​ ISCSI_TARGET_NAME=<​yourTargetName>​ ISCSI_TARGET_IP=<​yourTargetIp>​ ISCSI_TARGET_PORT=3260 quiet splash"​
 +</​code>​
  
-=== Stabilization/​Paranoia ===+=== Stabilization/​Paranoia/​Warnings ​===
  
 in order to prevent data loss (for example, a corrupted dpkg db), one may do the following stuff: in order to prevent data loss (for example, a corrupted dpkg db), one may do the following stuff:
  
   * 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. 
 +  * Additional warning: 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.

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