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I'm probably missing something, but since we are talking about data at
rest, can't we just have the OSD compress the object as it goes to
disk? Instead of
rbd\udata.1ba49c10d9b00c.0000000000006859__head_2AD1002B__11 it would
be rbd\udata.1ba49c10d9b00c.0000000000006859__head_2AD1002B__11.{gz,xz,bz2,lzo,etc}.
Then it seems that you don't have to muck with stripe sizes or
anything. For compressible objects they would be less than 4MB, some
of theses algorithms already say if it is not compressible enough,
just store it.
Something like zlib Z_FULL_FLUSH may help provide some seek points
within an archive to prevent decompressing the whole object for reads?
- ----------------
Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1
On Thu, Sep 24, 2015 at 10:25 AM, Igor Fedotov wrote:
>
>
> On 24.09.2015 19:03, Sage Weil wrote:
>>
>> On Thu, 24 Sep 2015, Igor Fedotov wrote:
>>
>> Dynamic stripe sizes are possible but it's a significant change from the
>> way the EC pool currently works. I would make that a separate project (as
>> its useful in its own right) and not complicate the compression situation.
>> Or, if it simplifies the compression approach, then I'd make that change
>> first. sage
>
> Just to clarify a bit. What I saw when played with Ceph. Please correct me
> if I'm wrong..
>
> For low-level RADOS access client data written to EC pool has to be aligned
> with stripe size . The last block can be unaligned though but no more
> appends are permitted in this case.
> Data copied from cache goes in blocks up to 8Mb size. In general case the
> last block seems to have unaligned size too.
>
> EC pool additionally performs alignment of the incoming blocks to stripe
> bound internally. This way blocks going to EC lib are always aligned.
> We should probably perform compression prior to this alignment.
> Thus some dependency on stripe size is present in EC pools but it's not that
> strict.
>
> Thanks,
> Igor
>
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