Re: Bareos and libradosstriper works only for 4M sripe_unit size

[Alexander Kushnirenko <kushnirenko@xxxxxxxxx>]

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@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxxx> 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

 

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