On 07/09/14 11:01 PM, Keith Keller wrote:
On 2014-09-08, Valeri Galtsev <galtsev@xxxxxxxxxxxxxxxxx> wrote:
Even more: system failure or power loss is more likely to destroy all data
on software RAID than on a single drive when there is a lot of IO present
(to the best of my understanding, loss of cache software RAID is using is
more catastrophic compared to journaled filesystem under same
circumstances - somebody may correct me). So, there may be worth thinking
about hardware RAID.
I think an essential feature of any md RAID that's not a RAID1 is a UPS
and a mechanism for a clean shutdown in case of extended power failure.
(An md RAID1 might be okay in this instance, but I wouldn't want to risk
it.) But this is true for any RAID, which is why many controllers come
with a BBU (and if you don't have a BBU on your hardware RAID controller,
then you absolutely need the UPS setup I described).
OTOH, the OP wasn't clear on what he was doing; perhaps he is just
playing around, and doesn't care about data preservation at this time.
If you're just testing performance then data integrity in the face of a
power failure is less of a concern.
--keith
A UPS is certainly better than nothing, but I would not consider it safe
enough. A BBU/FBU will protect you if the node loses power, right up to
the failure of the PSU(s). I've seen shorted cable harnesses taking out
servers with redundant power supplies, popped breakers in PDUs/UPSes,
knocked out power cords, etc. So a UPS is not a silver-bullet to safe
write-back caching in software arrays. Good, yes, but not perfect.
--
Digimer
Papers and Projects: https://alteeve.ca/w/
What if the cure for cancer is trapped in the mind of a person without
access to education?
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