[CentOS] OT: Caching synchronous writes

Fri Apr 23 00:08:06 UTC 2010
Ray Van Dolson <rayvd at bludgeon.org>

On Thu, Apr 22, 2010 at 03:57:01PM -0700, nate wrote:
> John R Pierce wrote:
> > Ray Van Dolson wrote:
> >>> I think what you want is a proper storage array with mirrored write
> >>> cache.
> >>>
> >>
> >> Which is what we have with ZFS + SSD-based ZIL for far less money than
> >> a NetApp.
> >>
> >
> > not unless you have a pair of them configured as an active/standby HA
> > cluster, sharing dual port disk storage, and some how (magic?) mirroring
> > the cache pool so that if the active storage controller/server fails,
> > the standby can take over wthout losing a single write.
> >
> OT too but really thought this was a good post/thread on ZFS
> http://www.mail-archive.com/zfs-discuss@opensolaris.org/msg18898.html
> "ZFS is designed for high *reliability*"
> [..]
> "You want something  completely different. You expect it to deliver
> *availability*.
> And availability is something ZFS doesn't promise. It simply can't
> deliver this."

Yep... and something you of course know going in.

Don't want to get off on a tangent on that -- am still interested what
type of solutions in the Linux world are out there that can approximate
what an SSD based ZIL does for ZFS.

Kent Overstreet (from lkml) mentioned that his bcache patch is intented
to do something very similar.

So I guess that's my answer -- it's not here yet, so sounds like the
controller is the only way to achieve this currently.