On 12/27/2014 02:32 AM, Lindsay Mathieson wrote:
I see a lot of people mount their xfs osd's with nobarrier for extra
performance, certainly it makes a huge difference to my small system.
However I don't do it as my understanding is this runs a risk of data
corruption in the event of power failure - this is the case, even with ceph?
side note: How do I tell if my disk cache is battery backed? I have WD Red 3TB
(WD30EFRX-68EUZN0) with 64M cache, but no mention of battery backup in the
docs. I presume that means it isn't? :)
You should never use "nobarrier" for xfs or ext4 - we worked hard to make the
difference negligible when the hardware has non-volatile caches, so it is easy
to default to the safe, barrier enabled mode.
Getting the data safely to disk is complicated, even with a battery backed RAID
card you can be exposed to data loss (if the actual drives have the write cache
enabled and your HBA does not manage that appropriately).
Regards,
Ric
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