Re: can't attach caching device to backing device

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On Mon, Nov 21, 2011 at 01:51:00PM +0000, Justin Rush wrote:
> Yes, the file does exist.

Hmm. Weird. I'll look at the code and see if I can think of anything.

> Should I try it with the individual devices in the array?

Worth a shot, though caching partitions is well tested. 

> I don't suppose bcache can play with LVM?

The version I just pushed should now.
> 
> - Justin
> 
> -----Original Message----- 
> From: Kent Overstreet [kent.overstreet@xxxxxxxxx]
> Received: Sunday, 20 Nov 2011, 11:31pm
> To: Justin Rush [jarush@xxxxxxxx]
> CC: linux-bcache@xxxxxxxxxxxxxxx [linux-bcache@xxxxxxxxxxxxxxx]
> Subject: Re: can't attach caching device to backing device
> When you tried to attach the cache, did the file you were echoing to
> exist? That looks correct but I'm not sure what else would generate
> that error.
> 
> For the UUIDs to show up in blkid, blkid itself would have to be
> updated to know about the bcache superblock (IIRC it lives in
> util-linux). I should probably ping the author and see if that can get
> included.
> 
> If you have the udev rules and probe-bcache installed, the symlinks
> /ought/ to show up when you reboot but I haven't tested that in ages.
> 
> I just got the code written so that it ought to be able to work on top
> of md devices again, which means I should be able to run it at home
> and I'll have to fix probe-bcache if it's broken then :)
> 
> On Mon, Nov 14, 2011 at 3:10 PM, Justin Rush <jarush@xxxxxxxx> wrote:
> > Using 3.1.0-rc9
> >
> > I created a cache device on /dev/sdk1
> > # ./make-bcache -C -b512k -w4k --writeback /dev/sdk1
> >
> > and a backing device on /dev/md127p1.
> > ./make-bcache -B /dev/md127p1
> >
> > # ./probe-bcache /dev/sdk1
> > 5f42bdd1-4342-4ab6-8dda-855989a09604: UUID="" TYPE="bcache"
> >
> > # ./probe-bcache /dev/md127p1
> > 6bbac9a4-afbd-4d40-9562-cdd290622c5d: UUID="" TYPE="bcache"
> >
> > I then registered them by:
> > # echo /dev/sdk1 >/sys/fs/bcache/register # echo /dev/md127p1 >/sys/fs/bcache/register
> >
> > I have /dev/bcache0
> >
> > When I try to attach the cache, I get this:
> > # echo "5f42bdd1-4342-4ab6-8dda-855989a09604" >/sys/block/md127/md127p1/bcache/attach
> > -bash: echo: write error: No such file or directory
> >
> > I believe this problem is due to the UUIDs for the two devices, but this is just a guess.  The UUID for /dev/sdk1 and /dev/md127p1 doesn't appear to be registering properly as they don't show up in blkid.  I tried specifying the UUID to use with the -U option when creating the devices, but that didn't seem to help.  I do have the udev rules file from the tools in place
> >
> > Does anyone know what is going on here and how to fix it?
> >
> > Justin Rush
> > jarush@xxxxxxxx
> >
> >
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