Greg Freemyer wrote:
The above youtube documents someone (like me) trying to use SMR drives not designed for RAID use in a raid array. The raid array apparently started kicking the SMR drives out of the array aggressively because of the very slow i/o speeds.
Thanks for the summary. I'd like to add. Don't use desktop drives for a RAID. **If** they work (like under a linux SW RAID, instead of w/a HW RAID), they'll be slower and strained. Someone asks why... Not knowing about this, some time ago, got some good desktop drives for a 5 disk SW RAID5. Wasn't more than a few months before it went bad, and performance was barely over a 1 disk write rate (1 disk ~ 100-120(MB/s) linear write), while the 4-data disk RAID couldn't read faster than 200-300 nor write faster than about 150. Very poor performance, IMO. I accidently ordered about 24 Hitachi Deskstars instead of Ultrastars (seller mixed them in w/offers for Ultrastars and might have been hoping no one would notice, not sure). But I decided to try them anyway. Out of 24 drives, 4 were "good" for HW RAID on an LSI card. I don't know *all* of the tests the LSI cards do on disks to determine good/bad, BUT at least one it must do, is whether or not the disks spin at the rated speed. In copying data, I found that the disks varied in spin speed by 20-25% in the worst cases. I.e. instead of 7200 RPM, the slow disks came in at about 6480 and the fast disks came in at about 8280. A single-disk desktop user probably wouldn't have noticed the difference -- maybe in the extremes, but putting them in a RAID... One disk spins almost 28% faster than the other, meaning any writes you do to the disks won't be able to be written out at the same time since the area to be written won't line up (due to constant speed differential). Sent all the disks back (I ate shipping), and ordered new Ultrastars -- more expensive, but worth it (especially now w/5-year replacement warranty). Tested them -- zero were kicked out as non-conforming and all of them ran at the same speed (I assume 7200, but no way to directly measure, really). If you really want the speed in your RAID -- even RAID1, get the more expensive enterprise disks. Imagine a 2 disk RAID1 where the disks have a 25% speed differential. That means they will only line up every 20 revolutions, or about 6 times/second. Compare 167ms to listed seek times (<10) and you can see the possible loss for write (read shouldn't be affected, as it only needs to read one of them). But if you went to a RAID0 or RAID10, RAID speed relies on being able to read & write to each disk in the same amount of time. If disks are off by 25%... this is not good! Let the buyer beware! -l -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org