Re: qemu-img convert vs rbd import performance

[Jason Dillaman <jdillama@xxxxxxxxxx>]

Running a similar 20G import test within a single OSD VM-based cluster, I see the following:

 

$ time qemu-img convert -p -O raw -f raw  ~/image rbd:rbd/image

    (100.00/100%)

real 3m20.722s

user 0m18.859s

sys 0m20.628s

$ time rbd import ~/image 

Importing image: 100% complete...done.

real 2m11.907s

user 0m12.236s

sys 0m20.971s

Examining the IO patterns from qemu-img, I can see that it is effectively using synchronous IO (i.e. only a single write is in-flight at a time), whereas "rbd import" will send up to 10 (by default) IO requests concurrently. Therefore, the higher the latencies to your cluster, the worse qemu-img will perform as compared to "rbd import". 

On Thu, Jul 20, 2017 at 5:07 AM, Mahesh Jambhulkar <mahesh.jambhulkar@xxxxxxxxx> wrote:

Adding  rbd readahead disable after bytes = 0  did not help.

[root@cephlarge mnt]# time qemu-img convert -p -O raw /mnt/data/workload_326e8a43-a90a-4fe9-8aab-6d33bcdf5a05/snapshot_9f0cee13-8200-4562-82ec-1fb9f234bcd8/vm_id_05e9534e-5c84-4487-9613-1e0e227e4c1a/vm_res_id_24291e4b-93d2-47ad-80a8-bf3c395319b9_vdb/66582225-6539-4e5e-9b7a-59aa16739df1 rbd:volumes/24291e4b-93d2-47ad-80a8-bf3c395319b9     (100.00/100%)

real    4858m13.822s

user    73m39.656s

sys     32m11.891s

It took 80 hours to complete.

Also, its not feasible to test this with huge 465GB file every time. So I tested qemu-img convert with a 20GB file.

Parameters	Time taken
-t writeback	38mins
-t none	38 mins
-S 4k	38 mins
With client options mentions by Irek Fasikhov	40 mins

The time taken is almost the same.

On Thu, Jul 13, 2017 at 6:40 PM, Jason Dillaman <jdillama@xxxxxxxxxx> wrote:

On Thu, Jul 13, 2017 at 8:57 AM, Irek Fasikhov <malmyzh@xxxxxxxxx> wrote:
>      rbd readahead disable after bytes = 0


There isn't any reading from an RBD image in this example -- plus
readahead disables itself automatically after the first 50MBs of IO
(i.e. after the OS should have had enough time to start its own
readahead logic).

--
Jason

--

Regards,

mahesh j

--

Jason

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