[linux-lvm] Thin Pool Performance

[shankha]

Hi,
I had just one thin logical volume and running fio benchmarks. I tried
having the metadata on a raid0. There was minimal increase in
performance. I had thin pool zeroing switched on. If I switch off
thin pool zeroing initial allocations were faster but the final
numbers are almost similar. The size of the thin poll metadata LV was
16 GB.
Thanks
Shankha Banerjee


On Tue, Apr 19, 2016 at 4:11 AM, Zdenek Kabelac <zkabelac at redhat.com> wrote:
> Dne 19.4.2016 v 03:05 shankha napsal(a):
>>
>> Hi,
>> Please allow me to describe our setup.
>>
>> 1) 8 SSDS with a raid5 on top of it. Let us call the raid device :
>> dev_raid5
>> 2) We create a Volume Group on dev_raid5
>> 3) We create a thin pool occupying 100% of the volume group.
>>
>> We performed some experiments.
>>
>> Our random write operations dropped  by half and there was significant
>> reduction for
>> other operations(sequential read, sequential write, random reads) as
>> well compared to native raid5
>>
>> If you wish I can share the data with you.
>>
>> We then changed our configuration from one POOL to 4 POOLS and were able
>> to
>> get back to 80% of the performance (compared to native raid5).
>>
>> To us it seems that the lvm metadata operations are the bottleneck.
>>
>> Do you have any suggestions on how to get back the performance with lvm ?
>>
>> LVM version:     2.02.130(2)-RHEL7 (2015-12-01)
>> Library version: 1.02.107-RHEL7 (2015-12-01)
>>
>
>
> Hi
>
>
> Thanks for playing with thin-pool, however your report is largely
> incomplete.
>
> We do not see you actual VG setup.
>
> Please attach  'vgs/lvs'  i.e. thin-pool zeroing (if you don't need it keep
> it disabled), chunk size (use bigger chunks if you do not need snapshots),
> number of simultaneously active thin volumes in single thin-pool (running
> hundreds of loaded thinLV is going to loose battle on locking) , size of
> thin pool metadata LV -  is this LV located on separate device (you should
> not use RAID5 with metatadata)
> and what kind of workload you try on ?
>
> Regards
>
> Zdenek
>
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