Re: How to do replication right with SRP or remote storage?

[Sebastian Riemer <sebastian.riemer-EIkl63zCoXaH+58JC4qpiA@public.gmane.org>]

On 10.06.2013 14:44, Bart Van Assche wrote:
> On 06/10/13 14:05, Sebastian Riemer wrote:
>> Perhaps, I should collect all guys who require MD RAID-1 for remote
>> storage replication in order to put some pressure on Neil.
> 
> If I remember correctly one of the things Neil is trying to explain to
> md users is that when md is used without write-intent bitmap there is a
> risk of triggering a so-called write hole after a power failure ?

I'm not sure. Haven't seen something like this on the mailing list. Do
you have a reference from the archives?

I think this is handled by superblock writes in the correct order by
now. The main reason for the write-intent bitmap remains from my
knowledge that you need a full resync without it if a component device
is down for a short moment in time. It becomes faulty.
If you know that there can't be a hardware issue (e.g. virtual storage),
you can remove the faulty device and re-add it to the array.

If a device was faulty, then it assembles again. There is an error
counter in /sys/block/mdX/md/ sysfs and a maximum read error count
(usually 20) after which the faulty device doesn't assemble again.

/sys/block/mdX/md/dev-Y/errors
/sys/block/mdX/md/max_read_errors

Cheers,
Sebastian
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