[ceph-users] Bareos and libradosstriper works only for 4M sripe_unit size

Christian Wuerdig christian.wuerdig at gmail.com
Mon Oct 16 16:59:56 PDT 2017


Maybe an additional example where the numbers don't line up all so
nicely would be good as well. For example it's not immediately obvious
to me what would happen with the stripe settings given by your example
but you write 97M of data
Would it be 4 objects of 24M and 4 objects of 250KB? Or will the last
4 objects be artificially padded (with 0's) to meet the stripe_unit?



On Tue, Oct 17, 2017 at 12:35 PM, Alexander Kushnirenko
<kushnirenko at gmail.com> wrote:
> Hi, Gregory, Ian!
>
> There is very little information on striper mode in Ceph documentation.
> Could this explanation help?
>
> The logic of striper mode is very much the same as in RAID-0.  There are 3
> parameters that drives it:
>
> stripe_unit - the stripe size  (default=4M)
> stripe_count - how many objects to write in parallel (default=1)
> object_size  - when to stop increasing object size and create new objects.
> (default =4M)
>
> For example if you write 132M of data (132 consecutive pieces of data 1M
> each) in striped mode with the following parameters:
> stripe_unit = 8M
> stripe_count = 4
> object_size = 24M
> Then 8 objects will be created - 4 objects with 24M size and 4 objects with
> 8M size.
>
> Obj1=24M    Obj2=24M    Obj3=24M    Obj4=24M
> 00 .. 07         08 .. 0f         10 .. 17         18 .. 1f  <-- consecutive
> 1M pieces of data
> 20 .. 27         21 .. 2f         30 .. 37         38 .. 3f
> 40 .. 47         48 .. 4f         50 .. 57         58 .. 5f
>
> Obj5= 8M    Obj6= 8M    Obj7= 8M    Obj8= 8M
> 60 .. 67        68 .. 6f        70 .. 77        78 .. 7f
>
> Alexander.
>
>
>
>
> On Wed, Oct 11, 2017 at 3:19 PM, Alexander Kushnirenko
> <kushnirenko at gmail.com> wrote:
>>
>> Oh!  I put a wrong link, sorry  The picture which explains stripe_unit and
>> stripe count is here:
>>
>>
>> https://indico.cern.ch/event/330212/contributions/1718786/attachments/642384/883834/CephPluginForXroot.pdf
>>
>> I tried to attach it in the mail, but it was blocked.
>>
>>
>> On Wed, Oct 11, 2017 at 3:16 PM, Alexander Kushnirenko
>> <kushnirenko at gmail.com> wrote:
>>>
>>> Hi, Ian!
>>>
>>> Thank you for your reference!
>>>
>>> Could you comment on the following rule:
>>> object_size = stripe_unit * stripe_count
>>> Or it is not necessarily so?
>>>
>>> I refer to page 8 in this report:
>>>
>>>
>>> https://indico.cern.ch/event/531810/contributions/2298934/attachments/1358128/2053937/Ceph-Experience-at-RAL-final.pdf
>>>
>>>
>>> Alexander.
>>>
>>> On Wed, Oct 11, 2017 at 1:11 PM, <ian.johnson at stfc.ac.uk> wrote:
>>>>
>>>> Hi Gregory
>>>>
>>>> You’re right, when setting the object layout in libradosstriper, one
>>>> should set all three parameters (the number of stripes, the size of the
>>>> stripe unit, and the size of the striped object). The Ceph plugin for
>>>> GridFTP has an example of this at
>>>> https://github.com/stfc/gridFTPCephPlugin/blob/master/ceph_posix.cpp#L371
>>>>
>>>>
>>>>
>>>> At RAL, we use the following values:
>>>>
>>>>
>>>>
>>>> $STRIPER_NUM_STRIPES 1
>>>>
>>>> $STRIPER_STRIPE_UNIT 8388608
>>>>
>>>> $STRIPER_OBJECT_SIZE 67108864
>>>>
>>>>
>>>>
>>>> Regards,
>>>>
>>>>
>>>>
>>>> Ian Johnson MBCS
>>>>
>>>> Data Services Group
>>>>
>>>> Scientific Computing Department
>>>>
>>>> Rutherford Appleton Laboratory
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> ceph-users mailing list
>>>> ceph-users at lists.ceph.com
>>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>>>>
>>>
>>
>
>
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