Re: [linux-lvm] Thin Pool Performance

[Zdenek Kabelac <zkabelac@redhat.com>]

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