Hello,
> Hello,
>
> we are currently investigating possiblities and performance limits of
> the Btrfs filesystem. Now it seems we are getting pretty poor
> performance for the writes and I would like to ask, if our results
> makes sense and if it is a result of some well known performance
> bottleneck.
>
> Our setup:
>
> Server:
> CPU: dual socket: E5-2630 v2
> RAM: 32 GB ram
> OS: Ubuntu server 14.10
> Kernel: 3.19.0-031900rc2-generic
> btrfs tools: Btrfs v3.14.1
> 2x LSI 9300 HBAs - SAS3 12/Gbs
> 8x SSD Ultrastar SSD1600MM 400GB SAS3 12/Gbs
>
> Both HBAs see all 8 disks and we have set up multipathing using
> multipath command and device mapper. Then we using this command to
> create the filesystem:
>
> mkfs.btrfs -f -d raid10 /dev/mapper/prm-0 /dev/mapper/prm-1
> /dev/mapper/prm-2 /dev/mapper/prm-3 /dev/mapper/prm-4
> /dev/mapper/prm-5 /dev/mapper/prm-6 /dev/mapper/prm-7
>
>
> We run performance test using following command:
>
> fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1
> --name=test1 --filename=test1 --bs=4k --iodepth=32 --size=12G
> --numjobs=24 --readwrite=randwrite
Could you check how many extents with BTRFS and Ext4:
# filefrag test1
To see if this is because bad fragments for BTRFS. I am still not
sure how fio will test randwrite here, so here is possibilities:
case1:
if fio don’t repeat write same position for several time, i think
you could add --overite=0, and retest to see if it helps.
case2:
if fio randwrite did write same position for several time, i think
you could use ‘-o nodatacow’ mount option to verify if this is because
BTRFS COW caused serious fragments.
>
>
> The results for the random read are more or less comparable with the
> performance of EXT4 filesystem, we get approximately 300 000 IOPs for
> random read.
>
> For random write however, we are getting only about 15 000 IOPs, which
> is much lower than for ESX4 (~200 000 IOPs for RAID10).
>
>
> Regards,
> Premek
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Best Regards,
Wang Shilong
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