Re: Poor RBD performance as LIO iSCSI target

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Thanks guys. I looked at http://tracker.ceph.com/issues/8818 and chatted with "dis" on #ceph-devel.

I ran a LOT of tests on a LOT of comabination of kernels (sometimes with tunables legacy). I haven't found a magical combination in which the following test does not hang:
fio --name=writefile --size=100G --filesize=100G --filename=/dev/rbd0 --bs=1M --nrfiles=1 --direct=1 --sync=0 --randrepeat=0 --rw=write --refill_buffers --end_fsync=1 --iodepth=200 --ioengine=libaio

Either directly on a mapped rbd device, on a mounted filesystem (over rbd), exported through iSCSI.. nothing.
I guess that rules out a potential issue with iSCSI overhead.

Now, something I noticed out of pure luck is that I am unable to reproduce the issue if I drop the size of the test to 50GB. Tests will complete in under 2 minutes.
75GB will hang right at the end and take more than 10 minutes.

TL;DR of tests:
- 3x fio --name=writefile --size=50G --filesize=50G --filename=/dev/rbd0 --bs=1M --nrfiles=1 --direct=1 --sync=0 --randrepeat=0 --rw=write --refill_buffers --end_fsync=1 --iodepth=200 --ioengine=libaio
-- 1m44s, 1m49s, 1m40s

- 3x fio --name=writefile --size=75G --filesize=75G --filename=/dev/rbd0 --bs=1M --nrfiles=1 --direct=1 --sync=0 --randrepeat=0 --rw=write --refill_buffers --end_fsync=1 --iodepth=200 --ioengine=libaio
-- 10m12s, 10m11s, 10m13s

Details of tests here: http://pastebin.com/raw.php?i=3v9wMtYP

Does that ring you guys a bell ?

--
David Moreau Simard


> On Nov 13, 2014, at 3:31 PM, Mike Christie <mchristi@xxxxxxxxxx> wrote:
> 
> On 11/13/2014 10:17 AM, David Moreau Simard wrote:
>> Running into weird issues here as well in a test environment. I don't have a solution either but perhaps we can find some things in common..
>> 
>> Setup in a nutshell:
>> - Ceph cluster: Ubuntu 14.04, Kernel 3.16.7, Ceph 0.87-1 (OSDs with separate public/cluster network in 10 Gbps)
>> - iSCSI Proxy node (targetcli/LIO): Ubuntu 14.04, Kernel 3.16.7, Ceph 0.87-1 (10 Gbps)
>> - Client node: Ubuntu 12.04, Kernel 3.11 (10 Gbps)
>> 
>> Relevant cluster config: Writeback cache tiering with NVME PCI-E cards (2 replica) in front of a erasure coded pool (k=3,m=2) backed by spindles.
>> 
>> I'm following the instructions here: http://www.hastexo.com/resources/hints-and-kinks/turning-ceph-rbd-images-san-storage-devices
>> No issues with creating and mapping a 100GB RBD image and then creating the target.
>> 
>> I'm interested in finding out the overhead/performance impact of re-exporting through iSCSI so the idea is to run benchmarks.
>> Here's a fio test I'm trying to run on the client node on the mounted iscsi device:
>> fio --name=writefile --size=100G --filesize=100G --filename=/dev/sdu --bs=1M --nrfiles=1 --direct=1 --sync=0 --randrepeat=0 --rw=write --refill_buffers --end_fsync=1 --iodepth=200 --ioengine=libaio
>> 
>> The benchmark will eventually hang towards the end of the test for some long seconds before completing.
>> On the proxy node, the kernel complains with iscsi portal login timeout: http://pastebin.com/Q49UnTPr and I also see irqbalance errors in syslog: http://pastebin.com/AiRTWDwR
>> 
> 
> You are hitting a different issue. German Anders is most likely correct
> and you hit the rbd hang. That then caused the iscsi/scsi command to
> timeout which caused the scsi error handler to run. In your logs we see
> the LIO error handler has received a task abort from the initiator and
> that timed out which caused the escalation (iscsi portal login related
> messages).

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