On Fri, Dec 14, 2012 at 01:51:19PM -0800, Darrick J. Wong wrote:
> Yeah, I think I've seen some odd behavior too - on one of my runs, blkid
> reported that the cache device had the same superblock as the aggregate device.
> My guess is that block 0 on the exported device got mapped to block 0 of the
> cache. I'll see if I can make it happen again, but that brings me to another
> set of questions.
This is normal.
> First, is there a plan to have userspace tools to set up the cache, provide
> protective superblocks, etc.?
Yes, lvm2 will support it soon (hopefully). Tools like cache_check,
cache_dump, cache_restore that manipulate the metadata device are
nearly ready.
> As far as I can tell, the slow disk and the fast
> disk don't have headers to declare the existence of the cache, so blkid and
> friends can end up seeing things they shouldn't. How were you planning to keep
> users from mounting the slow device before the cache comes up?
We don't label the origin device or ssd in anyway.
> Second, if the cache is in WB mode, is there a way to force it to flush the
> cache contents to disk? Or does it do that at dmsetup create time?
Reload the cache target with the cleaner policy. Once it's finished
writing everything back it'll trigger a dm event that you can catch
with 'dmsetup wait'. Then check the status to double check there
are no dirty blocks. At this point you can ditch the cache and use
the origin directly. See test below.
def wait_for_all_clean(cache)
cache.event_tracker.wait(cache) do |cache|
status = CacheStatus.new(cache)
status.nr_dirty == 0
end
end
def test_cleaner_policy
with_standard_cache(:format => true) do |cache|
git_prepare(cache, :ext4)
cache.pause do
table = cache.active_table
table.targets[0].args[6] = 'cleaner'
cache.load(table)
end
wait_for_all_clean(cache)
end
# We should be able to use the origin directly now
with_standard_linear do |origin|
fs = FS::file_system(:ext4, origin)
fs.with_mount('./kernel_builds', :discard => true) do
# triggers fsck
end
end
end
- Joe
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
