On Wed, 27 Jun 2007 15:06:31 +0200 Stuart Murray-Smith wrote: > > What is the preferred/most reliable level to implement software RAID > on a Fedora 7 server? Some thoughts to add to what has already been said: - Raid 1 is expensive on a cost-per-gigabyte basis. Although it's usually used in a two-bank configuration, there is no reason why you have to stop at two copies of your data -- you could have three or four copies if you wanted. If the disks are on separate controllers, you can read and write them in parallel, yielding good performance (1x write, Nx read). - Raid 5 provides a good cost-per-gigabyte, because only one drive is storing redundant information for each stripe. The write performance is worse than raid-1 and worse than a single drive, but the read performance is somewhere between a single drive and raid-1 (you can read in parallel, but not every drive has every block). - Raid 6 is like raid 5 with extra paranoia. But in all of this, a few things to consider: - You'll want to use software raid managed by the kernel in all but the most extreme cases (where it may make sense to use hardware raid). The CPU overhead is minimal on a modern system. Avoid motherboard raid, since it is in most cases a type of software raid that's tied to the motherboard BIOS. Using the kernel raid facilities gives you maximum flexibility in the case of a hardware failure (and resulting crisis): you won't need a source a particular motherboard model and software version or a special disk controller to recover your data. - If you're really paranoid, buy different brands or at least different batches of disks. There have been cases where several disks of the same brand fail within a very short time of each other (see for example http://tinyurl.com/34rrlo ) which can lead to irrecoverable data loss. - Hot spares enable a drive array to be rebuilt without your intervention. - Don't forget power supplies and controllers as possible points of failure. Power supplies are particularly bad because a failure can take out multiple drives plus the controller(s). - Obviously raid is no substitute for backup, because it doesn't protect against lightning strikes, fire, server theft, data corruption due to bugs, or user stupidity. -- Chris Tyler http://dailypackage.fedorabook.com
