RE: can't attach caching device to backing device

Great, I'll try the new code when I get home since the end goal is to use LVM on top of the raid devices and then present the LVs (or /dev/bcach*) to tcm/lio.

If there is any debug information I can give you, please let me know.

- Justin


-----Original Message-----
From: Kent Overstreet [mailto:koverstreet@google.com] 
Sent: Monday, November 21, 2011 7:54 AM
To: Justin Rush
Cc: kent.overstreet@gmail.com; linux-bcache@vger.kernel.org
Subject: Re: can't attach caching device to backing device

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@gmail.com]
Received: Sunday, 20 Nov 2011, 11:31pm
To: Justin Rush [jarush@epic.com]
CC: linux-bcache@vger.kernel.org [linux-bcache@vger.kernel.org]
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 [off-list ref] wrote:

quoted

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 

quoted

/sys/fs/bcache/register

I have /dev/bcache0

When I try to attach the cache, I get this:
# echo "5f42bdd1-4342-4ab6-8dda-855989a09604" 

quoted

/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@epic.com


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