On Wed, 14 Apr 2010 09:35:38 +0100 Chris Webb <chris@xxxxxxxxxxxx> wrote: > Hi. I have a linux cluster using tgtd as a target and openiscsi as an > initiator. At the moment, before export, I do something like > > tgtadm -L iscsi -m logicalunit -o update -t $TID -l 1 -P mode_page=8:0:18:0x10:0:0xff:0xff:0:0:0xff:0xff:0xff:0xff:0x80:0x14:0:0:0:0:0:0 > > to disable writeback caching on the target host. I'm wondering about > dropping this, but I don't properly understand how iscsi handles > write-caching at the target and therefore whether this is safe or not. > > If the target host crashes or suffers a power failure and is then restarted, > the initiator will continue where it left off, but data in the target's > writeback cache (presumably just page cache?) will have been lost. > > Will the initiator have retained the data that hadn't reached disk and > understand that it needs to resend, or will the volume end up corrupted with > the initiator's page cache not matching the real content on the disk? I think that it depends on what you run on the initiator. For example, when many file systems (such as ext3) hits a nexus loss (the target crashes), makes the disk offline. Then the page cache on the initiator will be lost. Note that data corruption is different from data loss. -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
