Re: [dm-devel] [RFC] A SCSI fault injection framework using SystemTap.

2008-01-15 Thread Alasdair G Kergon 
On Tue, Jan 15, 2008 at 12:04:09PM +0900, K.Tanaka wrote:
   -dm-mirror's redundancy doesn't work. A read error from the disk consisting
the array will be directory passed to the userspace, without reading from
the other mirror.
(It turns out that this issue is a known issue, but the patch is not 
 merged.
 
 http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/dm-raid1-handle-read-failures.patch)
 
It's in the queue for 2.6.25.

Alasdair
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Re: stride / stripe alignment on LVM ?

2007-11-11 Thread Alasdair G Kergon 
On Wed, Nov 07, 2007 at 10:00:39AM +0100, Goswin von Brederlow wrote:
 I would just check with dmsetup table dev to which byte offsets the
 logical volume gets mapped to.
 
Or use:
  pvs -o+pe_start
(optionally with --units)

Alasdair
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Re: [lvm-devel] [PATCH] lvm2 support for detecting v1.x MD superblocks

2007-10-23 Thread Alasdair G Kergon 
On Tue, Oct 23, 2007 at 11:32:56AM -0400, Mike Snitzer wrote:
 I've tested the attached patch to work on MDs with v0.90.0, v1.0,
 v1.1, and v1.2 superblocks.
 
I'll apply this, thanks, but need to add comments (or reference) to explain
what the hard-coded numbers are:

sb_offset = (size - 8 * 2)  ~(4 * 2 - 1);
etc.

Alasdair
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Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

2007-05-30 Thread Alasdair G Kergon 
On Wed, May 30, 2007 at 11:12:37AM +0200, Stefan Bader wrote:
 it might be better to indicate -EOPNOTSUPP right from
 device-mapper.
 
Indeed we should.  For support, on receipt of a barrier, dm core should
send a zero-length barrier to all active underlying paths, and delay
mapping any further I/O.

Alasdair
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Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

2007-05-30 Thread Alasdair G Kergon 
On Thu, May 31, 2007 at 10:46:04AM +1000, Neil Brown wrote:
 What if the truth changes (as can happen with md or dm)?

You get notified in endio() that the barrier had to be emulated?
 
Alasdair
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Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

2007-05-30 Thread Alasdair G Kergon 
On Thu, May 31, 2007 at 10:46:04AM +1000, Neil Brown wrote:
 If a filesystem cares, it could 'ask' as suggested above.
 What would be a good interface for asking?

XFS already tests:
  bd_disk-queue-ordered == QUEUE_ORDERED_NONE

Alasdair
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