Re: OSDs don't actually delete files when two CephFS (or more) are in use

[Sam Lang <sam.lang@inktank.com>]

On 12/10/2012 10:34 AM, Geoffrey Hartz wrote:
> Hi.
>
> I wait about more than 15 minutes. I was doing some benchmark when I
> noticed that the space never go back to normal..
>
> How can I disable this behavior? It's on Ceph side?
>
> With one client, OSD are cleaned after few seconds, this sounds normal

Actually after discussing with Greg and Sage, it sounds like this is a 
bug.  The issue is that the client that didn't remove the file is 
caching the dentry indefinitely.  I've created a ticket to track the 
issue here:  http://tracker.newdream.net/issues/3601.

Unfortunately, I don't think there's a good workaround for the time 
being.  You can try to evict those cached dentries by creating/accessing 
a bunch of other files, but the default cache size on the client is 
16384, which is a lot of files to touch just to free up the space for 
those removed files. :-)

You can decrease the cache size with the config option client_cache_size:

[client]
	client cache size = 128

Then you only have to create/touch 128 files to evict the other files 
from the cache.  That's not ideal, because reducing the cache size will 
affect your overall performance, but if you know that you won't be 
accessing a lot of files anyway, its probably your best bet.

-sam

>
> 2012/12/10 Sam Lang <sam.lang@inktank.com>:
>> On 12/10/2012 08:29 AM, Geoffrey Hartz wrote:
>>>
>>> Hi!
>>>
>>> I'm new to Ceph and I have a strange behavior with CephFS
>>>
>>> Config is :
>>>
>>> Ubuntu 12.04
>>> Kernel 3.6.9
>>> Ceph V0.55
>>>
>>> 2 OSD, 1 mon, 1 MDS, all on same host
>>> 2 clients, separate Hosts
>>>
>>> Ceph.conf:
>>>
>>> http://paste.ubuntu.com/1423712/
>>>
>>> To mount the share I use : sudo ceph-fuse -m 192.168.80.139:6789 /mnt
>>>
>>> When I create a file on one client, the other see the file, can be
>>> downloaded etc.
>>>
>>> But when I delete the file, both clients don't see the file anymore
>>> BUT the file is still there on OSD (using space disk).
>>
>>
>> Removing a file removes the directory entry (as you've seen), but the inode
>> itself doesn't get removed until all references to it are dropped.  The
>> clients may cache the capability for those inodes for a period of time, so
>> you're not seeing the references drop until they get evicted from the cache.
>> Unmounting ensures that they get evicted from the client caches, so all
>> references go to zero.
>>
>> Also, removal of the underlying objects is done lazily, so you may not see
>> the space get freed up right away.
>>
>> -sam
>>
>>>
>>> When I umount from BOTH clients, OSD are update and file is actually
>>> delete (same behavior with mount -t ceph)
>>>
>>> I'm missing something?
>>>
>>> Thanks!
>>>
>>> --
>>> Geoffrey HARTZ
>>> --
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>>>
>>
>
>
>