On Fri, Dec 12, 2014 at 2:53 PM, Wido den Hollander <wido@xxxxxxxx> wrote:
> On 12/12/2014 12:48 PM, Max Power wrote:
>> I am new to Ceph and start discovering its features. I used ext4 partitions
>> (also mounted with -o discard) to place several osd on them. Then I created an
>> erasure coded pool in this cluster. On top of this there is the rados block
>> device which holds also an ext4 filesystem (of course mounted with -o discard).
>>
>
> How are you using Ceph, Kernel RBD, Qemu/KVM?
>
>> I started to create some random 1MB files with tempfile and /dev/urandom to mess
>> the filesystem up and use all available space (256MB on my testdrive). After
>> this I deleted everything again. To my surprise the discard-feature did not
>> work. Ceph reports that ~256MB are used for data (after mkfs it was around 0MB).
>> I also tried to use 'fstrim' on the mountpoint but it reports that "the discard
>> operation is not supported". But why?
>>
>
> It depends. Kernel RBD does not support discard/trim yet. Qemu does
Just a note, discard support went into 3.18, which was released a few
days ago.
Thanks,
Ilya
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