On Sat, Dec 15, 2012 at 08:23:09AM +0000, Joe Thornber wrote:
> 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.
Are these tools available anywhere for testing?
--D
>
> > 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
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