On 07/09/14 10:43 PM, Valeri Galtsev wrote: > > On Sun, September 7, 2014 9:30 pm, John R Pierce wrote: >> On 9/7/2014 7:19 PM, Dave Stevens wrote: >>> I want to set up a new CentOS install using version 7 and would like >>> to experiment with various RAID levels. Anyone care to point out a >>> tutorial? >> >> how many drives do you have for this experiment? whats the target >> usecase for the file systems on the raid(s)? whats the level of data >> resiliance required by said use case? >> >> Raid only protects against one specific sort of failure, where an entire >> disk drive fails. It doesn't protect against data corruption, or >> system failure, > > 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. > > Just my 2c. > > Valeri Valeri makes an excellent point, which I would like to elaborate on; Hardware RAID *with* flash-backed/battery-backed cache. I find it endlessly fascinating how many machines out there have hardware RAID with BBU/FBU. When using write-back caching without a battery leaves you in no better position. Note that if you do get hardware RAID with BBU/FBU, be sure the cache policy is set to "Write-Back with BBU" (or your controllers wording). The idea here is that, if the battery/caps fail/drain, the controller switches to write-through (no) caching. I'm not so familiar with software RAID, but I would be surprised if there isn't a way to force write-through caching. If this is possible, then Valeri's concern can be addressed (at the cost of performance). digimer -- 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?