----- Original Message ----- > From: "Keith Keller" <kkeller at wombat.san-francisco.ca.us> > To: centos at centos.org > Sent: Thursday, April 11, 2013 4:34:20 PM > Subject: Re: [CentOS] RAID 6 - opinions > > On 2013-04-11, David C. Miller <millerdc at fusion.gat.com> wrote: > > > > Just for reference, I have a 24 x 2TB SATAIII using CentOS 6.4 > > Linux MD RAID6 with two of those 24 disks as hotspares. The drives > > are in a Supermicro external SAS/SATA box connected to another > > Supermicro 1U computer with an i3-2125 CPU @ 3.30GHz and 16GB ram. > > The connection is via a 6Gbit mini SAS cable to an LSI 9200 HBA. > > Before I deployed it into production I tested how long it would > > take to rebuild the raid from one of the hot spares and it took a > > little over 9 hours. > > I did a similar test on a 3ware controller. Apparently those cards > have > a feature that allows the controller to remember which sectors on the > disks it has written, so that on a rebuild it only reexamines those > sectors. This greatly reduces rebuild time on a mostly empty array, > but > it means that a good test would almost fill the array, then attempt a > rebuild. I definitely saw a difference in rebuild times as I filled > the > array. (In 3ware/LSI world this is sometimes called "rapid RAID > recovery".) > > In checking my archives, it looks like a rebuild on an almost full > 50TB > array (24 disks) took about 16 hours. That's still pretty > respectable. > I didn't repeat the experiment, unfortunately. > > I don't know if your LSI controller has a similar feature, but it's > worth investigating. > > --keith > The LSI 9200's I use are nothing more than a dumb $300 host bus adapter. No RAID levels or special features. I prefer to NOT use hardware RAID controllers when I can. With a generic HBA the hard drives are seen raw to the OS. You can use smartctl to poll and test the drives just like they were connected to a generic SATA bus on the motherboard. The tools built into Linux(smartd & md) are better suited and more flexible at reporting problems and handling every level of RAID. It also makes migrating the array to another system trivial. I don't have to worry about finding the exact same RAID controller. Just a no frills SAS/SATA HBA will do. David.