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Re: [ANNOUNCE] xfs: Supporting Host Aware SMR Drives

To: Alireza Haghdoost <haghdoost@xxxxxxxxx>
Subject: Re: [ANNOUNCE] xfs: Supporting Host Aware SMR Drives
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 17 Mar 2015 17:06:01 +1100
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Linux Filesystem Development List <linux-fsdevel@xxxxxxxxxxxxxxx>, linux-scsi <linux-scsi@xxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <CAB-428kqj2KChEGmjqSXLhM4TMM-dsgK7LzkQXxgp5En4jBVRg@xxxxxxxxxxxxxx>
References: <20150316060020.GB28557@dastard> <1426519733.4000.11.camel@xxxxxxxxxxxxxxxxxxxxx> <20150316203207.GD28557@dastard> <CAB-428kqj2KChEGmjqSXLhM4TMM-dsgK7LzkQXxgp5En4jBVRg@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Mar 16, 2015 at 08:12:16PM -0500, Alireza Haghdoost wrote:
> On Mon, Mar 16, 2015 at 3:32 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> > On Mon, Mar 16, 2015 at 11:28:53AM -0400, James Bottomley wrote:
> >> Probably need to cc dm-devel here.  However, I think we're all agreed
> >> this is RAID across multiple devices, rather than within a single
> >> device?  In which case we just need a way of ensuring identical zoning
> >> on the raided devices and what you get is either a standard zone (for
> >> mirror) or a larger zone (for hamming etc).
> >
> > Any sort of RAID is a bloody hard problem, hence the fact that I'm
> > designing a solution for a filesystem on top of an entire bare
> > drive. I'm not trying to solve every use case in the world, just the
> > one where the drive manufactures think SMR will be mostly used: the
> > back end of "never delete" distributed storage environments....
> > We can't wait for years for infrastructure layers to catch up in the
> > brave new world of shipping SMR drives. We may not like them, but we
> > have to make stuff work. I'm not trying to solve every problem - I'm
> > just tryin gto address the biggest use case I see for SMR devices
> > and it just so happens that XFS is already used pervasively in that
> > same use case, mostly within the same "no raid, fs per entire
> > device" constraints as I've documented for this proposal...
> I am confused what kind of application you are referring to for this
> "back end, no raid, fs per entire device". Are you gonna rely on the
> application to do replication for disk failure protection ?

Exactly. Think distributed storage such as Ceph and gluster where
the data redundancy and failure recovery algorithms are in layers
*above* the local filesystem, not in the storage below the fs.  The
"no raid, fs per device" model is already a very common back end
storage configuration for such deployments.


Dave Chinner

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