[dm-devel] [PATCH RFC] dm-raid1: keep writing after leg failure

[Brassow Jonathan]

> On Apr 2, 2015, at 10:51 PM, Lidong Zhong <lzhong at suse.com> wrote:
> 
> Currently if there is a leg failure, the bio will be put into the hold
> list until userspace replace/remove the leg. Here we are trying to make
> dm-raid1 ignore the failure and keep the following bios going on.
> This is because there maybe a temporary path failure in clvmd
> which leads to cluster raid1 remove/replace the fake device failure. And
> it takes a long time to do the full sync if we readd the device back.
> ---

Just be aware that there are failure scenarios that this does not handle as well.  Like a reboot causing the legs to return but not the log.  It’s a remote possibility, but something the old model considered.  The new RAID targets which leverage the MD personalities are much better (e.g. ‘lvcreate —type raid1’), but they don’t support active-active cluster setups.

I’ve seen a couple things on the linux-raid mailing list suggesting that someone (Goldwyn Rodrigues) may be thinking about making RAID1/10 cluster-aware…  LVM should be able to take advantage of this if it became a reality.

Are you interested in providing your use-case for cluster mirroring (vs opting for active/passive mirroring)?

 brassow