On 22/12/15 09:03, NeilBrown wrote:
On Tue, Dec 22 2015, Tejas Rao wrote:
On 12/21/2015 15:47, NeilBrown wrote:
On Tue, Dec 22 2015, Tejas Rao wrote:
What if the application is doing the locking and making sure that only 1
node writes to a md device at a time? Will this work? How are rebuilds
handled? This would be helpful with distributed filesystems like
GPFS/lustre etc.
You would also need to make sure that the filesystem only wrote from a
single node at a time (or access the block device directly). I doubt
GPFS/lustre make any promise like that, but I'm happy to be educated.
rebuilds are handled by using a cluster-wide lock to block all writes to
a range of addresses while those stripes are repaired.
NeilBrown
My understanding of MD level cross host RAID was that it would not
magically create cluster aware filesystems out of non-cluster aware
filesystems. ie, you wouldn't be able to use the same multi-host RAID
device on multiple hosts concurrently with ext3.
IMHO, if it was able to behave similar to DRBD, then that would be
perfect (ie, enforce only a single node can write at a time (unless you
specifically set it for multi-node write)). The benefit should be that
you can lose a node without losing your data. After you lose that node,
you can then "do something" to use the remaining node to access the data
(eg, mount it, export with iscsi/nfs, etc).
Currently, this is what I use DRBD for, previously, I've used NBD + MD
RAID1 to do the same thing. One question though is what advantage
multi-host MD RAID might have over the existing in-kernel DRBD ? Are
there plans which show why this is going to be better, have better
performance, features, etc?
Regards,
Adam
--
Adam Goryachev Website Managers www.websitemanagers.com.au
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