Re: layering question.

A. James Lewis
2015-08-07T16:16:21Z

OK, but in that case bcache is not between your MD RAID and it's disks,
so if your disks are dropping out of the MD array, that has to be either
an independent problem, or a very complex bug.

James

On 07/08/15 16:36, Jens-U. Mozdzen wrote:
> Hi James,
>
> Zitat von "A. James Lewis" <james@fsck.co.uk>:
>> That's interesting, are you putting your MD on top of multiple bcache
>> devices... rather than bcache on top of an MD device... I wonder what
>> the rationale behind this is?
>
> Hi James, no such thing here...
>
> bcache is running on top of two MD-RAIDs - RAID6 with 7 spinning
> drives and RAID1 with two SSDs.
>
> The stack is, from bottom to top:
>
> - MD-RAID6 data, MD-RAID1 cache
> - bcache (/dev/bcache0, used as an LVM PV)
> - LVM
> - many LVs
> - DRBD on top of most of the LVs
> - Ext4 on each of the DRBD devices
> - SCST / NFS / SMB sharing these file systems
>
> In the referenced incidents, SCST reports that (many) writes failed
> due to time-out, and MD reports a single disk faulty. No other traces
> in syslog, especially no stalled processes, locking problems or kernel
> bugs.
>
> The i/o pattern is highly parallel reads and writes, mostly via SCST.
>
> Regards,
> Jens
>
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