Andrei Borzenkov wrote:
On Wed, Dec 14, 2016 at 1:40 PM, Per Jessen
wrote: 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.
In principle it hasn't failed until you notice 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.
Usually SMART (and other vendor-specific diagnostics) tests are run regularly, that's about it.
We probably have different notion of "enterprise class hardware" ... :)
We use 3ware, HP and IBM. Yes, I know the latter two will scan for bad sectors during period of inactivity, but that's all. They don't go scrubbing down terabytes of data very often if at all. I don't know if the drive electronics does something like that?
If you cannot rely on your data being written accurately to your disk, all bets are off.
The fact that data had been accurately written to your disk in the past by no means imply that data can be accurately read today.
Very true, yet we all rely on exactly that. -- Per Jessen, Zürich (2.2°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org