> -----Original Message----- > From: matthew patton [mailto:pattonme@xxxxxxxxx] > Sent: mardi 28 janvier 2014 23:36 > To: Patrick Zwahlen; linux-bcache@xxxxxxxxxxxxxxx > Subject: Re: Moving a backing device between 2 cachesets > > > > >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 > >- 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. > >At this point, cacheset1 is attached to nothing, but still has valid > blocks > >"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 -
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