Fwd: Re: Merging CephFS data pools

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-------- Forwarded Message --------
Subject: Re: Merging CephFS data pools
Date: Tue, 23 Aug 2016 08:59:45 +0200
From: Burkhard Linke <Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
To: Gregory Farnum <gfarnum@xxxxxxxxxx>


Hi,


On 08/22/2016 10:02 PM, Gregory Farnum wrote:
> On Thu, Aug 18, 2016 at 12:21 AM, Burkhard Linke
> <Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hi,
>>
>> the current setup for CephFS at our site uses two data pools due to
>> different requirements in the past. I want to merge these two pools now,
>> eliminating the second pool completely.
>>
>> I've written a small script to locate all files on the second pool using
>> their file layout attributes and replace them with a copy on the correct
>> pool. This works well for files, but modifies the timestamps of the
>> directories.
>> Do you have any idea for a better solution that does not modify timestamps
>> and plays well with active CephFS clients (e.g. no problem with files being
>> used)? A simple 'rados cppool' probably does not work since the pool id/name
>> is part of a file's metadata and client will not be aware of moved
>> files.....
> Can't you just use rsync or something that will set the timestamps itself?
The script is using 'cp -a', which also preserves the timestamps. So 
file timestamps are ok, but directory timestamps get updated by cp and 
mv. And that's ok from my point of view.

The main concern is data integrity. There are 20TB left to be 
transferred from the old pool, and part of this data is currently in 
active use (including being overwritten in place). If write access to an 
opened file happens while it is being transfered, the changes to that 
file might be lost.

We can coordinate the remaining transfers with the affected users, if no 
other way exists.

Regards,
Burkhard
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