Re: [RFC][PATCH 1/2] Btrfs: try to allocate new chunks with degenerated profile

[Hugo Mills <hugo@carfax.org.uk>]

[-- Attachment #1: Type: text/plain, Size: 1386 bytes --]

On Wed, Jan 18, 2012 at 11:12:20AM +0100, Jan Schmidt wrote:
> On 17.01.2012 21:58, Chris Mason wrote:
> > These two didn't make my first pull request just because I wanted to get
> > something out the door.  I'll definitely have them in the next pull.
> 
> Please, don't do that! You can't just degenerate to DUP when RAID1 is
> out of space, that's entirely different.

   Agreed. This isn't a good idea.

> It's debatable whether degeneration from RAID0 to single is acceptable,
> but that again has different characteristics.

   RAID-0 to single and RAID-10 to RAID-1 are less controversial, I
think, although we need to be clear about what the performance
guarantees of the striping are (and how they would be affected by the
move to fewer disks). Given that we already degrade the striping of
RAID-0 down to "as many devices as we can fit right now", we're not
really providing much in the way of performance guarantees.

   (I'd definitely support some way of defining a fixed-width stripe,
but that's a whole separate question that we shouldn't get into now).

> ENOSPC is the best choice for both in my opinon.
> 
> -Jan

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
  PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
      --- What's a Nazgûl like you doing in a place like this? ---      

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 190 bytes --]