-----Original Message-----
From: matthew patton [mailto:pattonme@yahoo.com]
Sent: mardi 28 janvier 2014 23:36
To: Patrick Zwahlen; linux-bcache@vger.kernel.org
Subject: Re: Moving a backing device between 2 cachesets

quoted

Scenario
- md attached to cacheset1 and working (on node 1)
- md detached from cacheset1

You can't just detach, you must flush everything out of cacheset1 and
destroy/revoke/disassemble the relationship between the cache and MD.
'destroy-bcache(8) or make-bcache -D' if you will. Not that such a tool
exists AFAIK.

Doc says:
detach
  Write to this file to detach from a cache set. If there is dirty data in
the
  cache, it will be flushed first.

As we're in write-through mode, I don't care about dirty data

quoted

- md stopped on node 1
- md started on node 2
- md attached to cacheset2 on node 2

No, you don't attache it, you have to create a new relationship; ala
'make-bcache -C ...'

Hmmm. The local ssd (cacheset) is shared between multiple backing devices,
so having to "make-bcache -C" at this point is painful. 

quoted

At this point, cacheset1 is attached to nothing, but still has valid

blocks

quoted

"linked" to the backing md device

If you do, your data is hopelessly gone.

Again, write-through means all the writes should be safe. I mostly care
about reads that were cached in a previous cacheset and might be delivered
again.

The setup is maybe hard to describe, so for the sake of simplicity it can be
summarized like that:

One node with 2 independent SSDs configured as write-through cachesets (-C)
and multiple storage devices configured as backing devices (-B).

I want to be able to safely move any single backing device from one SSD to
the other (and vice-versa) in a safe way.

Would that work ?

Regards, - Patrick -