On 11/13/2013 09:13 AM, Matthew Patton wrote:
On Wed, 13 Nov 2013 03:42:54 -0500, Francis Moreau
<francis.moro@xxxxxxxxx> wrote:
And finally, can I create the over-provisioning without lost the
content of my backing device ?
hell no.
I'm a bit confused: why not? Francis seems to be asking if the entire
bcache device needs to be recreated. It definitely is necessary to
rebuild the cache device, but the backing device shouldn't be affected.
Let's call the backing device /dev/backdev and the cache device
/dev/cachedev. Then it should be possible to do the following:
0. If you are using writeback caching, "echo none >
/sys/block/backdev/bcache/cache_mode" to tell bcache to flush the
contents of the cache and then wait until "cat
/sys/block/backdev/bcache/dirty_data" yields a zero
1. "echo 1 > /sys/block/backdev/bcache/detach" to remove the caching
device from the bcache volume
2. "echo 1 > /sys/fs/bcache/$UUID/unregister" to remove the caching
device from the kernel
3. repartition the caching device so that /dev/cachedev is only e.g. 75%
of the SSD
4. "make-bcache -C /dev/cachedev" to recreate the cache device
5. "echo /dev/cachedev > /sys/fs/bcache/register" to make the kernel
aware of the new device
6. "ls /sys/fs/bcache" or just pay attention to make-bcache to find the
cache volume UUID
7. "echo $UUID > /sys/block/backdev/bcache/attach" to reattach the
caching device
8. "echo whatever-mode > /sys/block/backdev/bcache/cache_mode" to put it
back into whichever mode you wish
Is there something wrong with my reasoning? I may also have
misunderstood the situation. I'm just hoping I understand bcache as
well as I think I do. :)
Cheers,
Zach
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