Quoting Digimer <lists at alteeve.ca>: > On 07/09/14 11:01 PM, Keith Keller wrote: >> On 2014-09-08, Valeri Galtsev <galtsev at kicp.uchicago.edu> 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. This is a pretty interesting discussion but has not revealed an on-line tutorial. Anyone? Dave > > -- > 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? > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > -- We hang petty thieves and appoint great ones to office -- Aesop