Re: [PATCH] secure write for RAID1

[Lars Marowsky-Bree <lmb@suse.de>]

On 2005-04-27T13:24:36, Neil Brown <neilb@cse.unsw.edu.au> wrote:

> On Saturday April 23, ptb@lab.it.uc3m.es wrote:
> > This patch (completely untested of course - what, me?) makes RAID1 write
> > to all components of a raid-1 array, else return error to the write
> > attempt, when one component cannot be written.
> I don't understand why or when you would want this.
> 
> This wouldn't just return an error to the application if the write
> wasn't completely safe.  It would cause the filesystem to switch to
> read-only very quickly and make your machine un-usable.  Is that
> really what you want??

Databases sometimes want this (also for replication).

They'd rather fail than potentially lose a committed transaction, and to
that end they require that the data be written to at least two disks; ie
they want the data to be able to withstand at least one failure.  We've
had such a request from a big database vendor for drbd too.

(This however is a great application for >2 mirrors and a write quorum
of two, though.)


Sincerely,
    Lars Marowsky-Brée <lmb@suse.de>

-- 
High Availability & Clustering
SUSE Labs, Research and Development
SUSE LINUX Products GmbH - A Novell Business

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