hum let's keep practical here please. The question is whether you can use SATA RAID as a reasonable HD failure protection system or not. Can a Raid1 on two HD, say less than 500Gb, be consider as a good protection against HD failure? It still seems to be for me. (I consider recovery to be just a bit to bit copy, not sure to rigt here) On a Raid5, since there's need for computation in case of HD failure, it seems more discutable after the facts that you've exposed. It seems that this assumption needs statistics depending on HD size which I'm not able to produce. But with reasonably sized disk, it should still be ok, isn't it? Jeff Mohler wrote:
SATA drives just aint built with the same resiliency as SCSI, hence the massive difference in cost. So..as an example, the Hitachi 500G 7K500 drive has a non recoverable bitrate of 1 in 10^14th. The 10K300 FCAL (basically scsi) drive is 1 in 10^16th. Those two zeros mean a _lot_. I removed a lot of my own math here, knowing that Ive read this somewhere before..huzzah for google! [1]http://blogs.netapp.com/dave/2006/03/expect_double_d.html?no_prefetch=1 Im used to working with much larger drives, in very large RGs..so Im correctable, youre not going to play with the devil TOO much in a home for small business system, just not enough drives. But now you can find 1TB drives, and 7 of those in a raid wont be hard to find pretty soon. Eventually..you will hit a non recoverable bit error during a reconstruction, and you wont have parity to go to, to recover it. Unless youre using a dual parity layout of some type. Drives are also more common to fail when put into use from being spares, because theyve never been exercised over a long period of time..ya never know. The quality of the firmware that operates consumer SATA isnt near the level of quality that server drives are either, which can create ghost errors that dont truly exist, but to the OS are in fact errors which can shave off a few zeros as well. On 10/10/07, Nodje [2]<[EMAIL PROTECTED]> wrote: well, you mean on RAID5 then, coz there's probably no math in reconstructing a RAID1. Why would the math on SATA be less reliable than on SCSI??? Where d'you read that anyway?? Jeff Mohler wrote: Did you know that most "oh my god" RAID failures happen during the reconstruction of a failed drive? .Especially on SATA as the non-recoverable-bit-error math is so much easier to run into. I think..that on a 500G drive, there are enough bits to read/write that mathematically you could run into a double-drive failure every time you have to recover. Although, statistically it wouldnt happen every time. No raid solves any backup problem. I've been using those Intel RAID with Windows for a couple of years now and it really helped solve my backup problem. I think this is simply great, no worries of data loss anymore (at least coming from hardware failure). -nodje _______________________________________________ [EMAIL PROTECTED] mailing list [4]http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [5]"[EMAIL PROTECTED]" References 1. http://blogs.netapp.com/dave/2006/03/expect_double_d.html?no_prefetch=1 2. mailto:[EMAIL PROTECTED] 3. mailto:[email protected] 4. http://lists.freebsd.org/mailman/listinfo/freebsd-questions 5. mailto:[EMAIL PROTECTED]
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