On Jul 27, 2009, at 10:27 AM, Eric D. Mudama wrote:
On Sun, Jul 26 at 1:47, David Magda wrote:
On Jul 25, 2009, at 16:30, Carson Gaspar wrote:
Frank Middleton wrote:
Doesn't this mean /any/ hardware might have this problem, albeit
with much lower probability?
No. You'll lose unwritten data, but won't corrupt the pool,
because the on-disk state will be sane, as long as your iSCSI
stack doesn't lie about data commits or ignore cache flush commands.
But this entire thread started because Virtual Box's virtual disk /
did/ lie about data commits.
Why is this so difficult for people to understand?
Because most people make the (not unreasonable assumption) that
disks save data the way that they're supposed to: that the data
goes in is the data that comes out, and that when the OS tells them
to empty the buffer that they actually flush it.
It's only us storage geeks that generally know the ugly truth that
this assumption is not always true. :)
Can *someone* please name a single drive+firmware or RAID
controller+firmware that ignores FLUSH CACHE / FLUSH CACHE EXT
commands? Or worse, responds "ok" when the flush hasn't occurred?
two seconds with google shows
http://seagate.custkb.com/seagate/crm/selfservice/search.jsp?DocId=183771&NewLang=en&Hilite=cache+flush
Give it up. These things happen. Not much you can do about it, other
than design around it.
-- richard
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