On Wed, Dec 14, 2016 at 6:13 AM, Andrei Borzenkov
my main concern on raid is unused data control, that is verification of the integrity of unused data on disk (to prevent unexpected multi disk failure).
Huh? You mean check unused data or unused space? I don't see what you would gain
Consider RAID5 stripe D1, D2, P (two data blocks, one parity). D1 belongs some file and is accessed frequently. D2 happens to be outside of any file or metadata so never explicitly accessed by host.
If D1 is unreadable, it can be reconstructed from D2 and P. Because D1 (and P) are accessed often, there is good probability that problems will be noticed and corrected early. But you are not aware of state of D2 until the very moment you need it to reconstruct your data. If at this moment D2 is unreadable, data is lost. D2 may have failed years ago without you being aware of it.
and I am not aware of any enterprise class hardware that will do it.
*Every* enterprise class hardware performs periodical scrub across the full range of disk blocks to detect and fix latent errors. Most enterprise class hardware I am aware of performs permanent scrub and you cannot turn it off at all.
The discussion got me curious, and yes the Drobo does do background data scrubbing. "Drobo systems continuously scrub data in the background to fix disk errors before they happen. If there are too many errors, we proactively purge the drive and rebuilt using the available space on other drives. " Also, I can hear mine going to town write now, but there is no client activity at the moment so it should be idle. Greg -- Greg Freemyer -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org