Re: raid0: "clean" state on drive failure/removal

[NeilBrown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 2351 bytes --]

On Fri, 27 Feb 2015 20:54:32 +0000 Sushma Gurram <Sushma.Gurram@sandisk.com>
wrote:

> Hi,
> 
> A basic question on raid0 behavior.
> 
> When a drive fails/removed in a raid0 array, “mdadm –detail” reports the array
> state as clean instead of failed.
> 
> It appears that the drive is whacked out of the array, but that array slot
> continues to show “active sync” state.
> 
> I/O to the failed drive errors out. However, it appears that I/O to other drives
> in the raid0 array would succeed. How would the user know about the array state
> and potential data loss? Should the array information be cached, drive
> failure/removals be monitored and checked against the cached information?

The user would know about potential data loss in *exactly* they same way as
if half the sectors on a single hard-drive stopped working.

i.e. the filesystem would complain.

> 
> Could anyone please explain the reason for this behavior of not reporting a
> raid0 array as failed?

RAID0 is not really RAID - there is no redundancy.
So it isn't treated like RAID.

RAID0 is simply a mapping off linear addresses onto multiple devices.
There is no sense in which the array as a whole "fails", or any value in
marking a device as "failed".

If there is something wrong, then IO requests will fail.  Not necessarily all
IO requests, but some.  Just like a normal drive that has partially failed.

NeilBrown

> 
> Thanks,
> Sushma
> 
> ________________________________
> 
> PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. If the reader of this message is not the intended recipient, you are hereby notified that you have received this message in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify the sender by telephone or e-mail (as shown above) immediately and destroy any and all copies of this message in your possession (whether hard copies or electronically stored copies).
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]