On Thu, Feb 03, 2011 at 12:35:52PM -0200, Roberto Spadim wrote: > =] i think that we can end discussion and conclude that context (test > / production) allow or don't allow lucky on probability, what's lucky? > for production, lucky = poor disk, for production we don't allow > failed disks, we have smart to predict, and when a disk fail we change > many disks to prevent another disk fail > > could we update our raid wiki with some informations about this discussion? I would like to, but it is a bit complicated. Anyway I think there already is something there on the wiki. And then, for one of the most important raid types in Linux MD, namely raid10, I am not sure what to write. It could be raid1+0, or raid0+1 like, and as far as I kow, it is raid0+1 for F2:-( but I don't know for n2 and o2. The German version on raid at wikipedia has a lot of info on probability http://de.wikipedia.org/wiki/RAID - but it is wrong a number of places. I have tried to correct it, but the German version is moderated, and they don't know what they are writing about. http://de.wikipedia.org/wiki/RAID Best regards Keld > 2011/2/3 Drew <drew.kay@xxxxxxxxx>: > >> for test, raid1 and after raid0 have better probability to don't stop > >> raid10, but it's a probability... don't believe in lucky, since it's > >> just for test, not production, it doesn't matter... > >> > >> what i whould implement? for production? anyone, if a disk fail, all > >> array should be replaced (if without money replace disk with small > >> life) > > > > A lot of this discussion about failure rates and probabilities is > > academic. There are assumptions about each disk having it's own > > independent failure probability, which if that can not be predicted > > must be assumed to be 50%. At the end of the day I agree that when > > the first disk fails the RAID is degraded and one *must* take steps to > > remedy that. This discussion is more about why RAID 10 (1+0) is better > > then 0+1. > > > > On our production systems we work with our vendor to ensure the > > individual drives we get aren't from the same batch/production run, > > thereby mitigating some issues around flaws in specific batches. We > > keep spare drives on hand for all three RAID arrays, so as to minimize > > the time we're operating in a degraded state. All data on RAID arrays > > is backed up nightly to storage which is then mirrored off-site. > > > > At the end of the day our decision around what RAID type (10/5/6) to > > use was based on a balance between performance, safety, & capacity > > then on specific failure criteria. RAID 10 backs the iSCSI LUN that > > our VMware cluster uses for the individual OSes, and the data > > partition for the accounting database server. RAID 5 backs the > > partitions we store user data one. And RAID 6 backs the NASes we use > > for our backup system. > > > > RAID 10 was chosen for performance reasons. It doesn't have to > > calculate parity on every write so for the OS & database, which do a > > lot of small reads & writes, it's faster. For user disks we went with > > RAID 5 because we get more space in the array at a small performance > > penalty, which is fine as the users have to access the file server > > over the LAN and the bottle neck is the pipe between the switch & the > > VM, not between the iSCSI SAN & the server. For backups we went with > > RAID 6 because the performance & storage penalties for the array were > > outweighed by the need for maximum safety. > > > > > > > > -- > > Drew > > > > "Nothing in life is to be feared. It is only to be understood." > > --Marie Curie > > > > > > > > -- > Roberto Spadim > Spadim Technology / SPAEmpresarial > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
