Hi, Sorry, I forget to provide more information on my system configuration. I use Ubuntu 13.10 and update linux kernel to 3.13.3. The dmsetup table output should be similar in all experiments as follow: thin: 0 80000000 thin 252:0 0 pool: 0 117433344 thin-pool 8:145 9:0 2048 0 1 skip_block_zeroing Thanks, Dennis 2014-02-18 17:34 GMT+08:00 Zdenek Kabelac <zkabelac@xxxxxxxxxx>: > Dne 18.2.2014 10:13, Teng-Feng Yang napsal(a): > >> Dear all, >> >> I have been working on tuning the dm-thin performance on my storage >> server. >> I surprisingly find out that the write performance of newly created >> thin volume formatted as EXT4 has degraded significantly, when >> building thin-pool on top of RAID6 device. >> Thin pools in all experiment use 1MB block size, and I format all >> target volumes as EXT4 and mount them on /mnt. >> The following is the performance statistics I gather under different >> circumstances. >> >> Thin volume on top of a thin pool created by a Plextor M5P 128GB SSD >> as metadata device >> and a RAID6 block device composed by 7 disks (chunk size = 512KB) as a >> data device >> dennis@desktop:~$ sudo dd if=/dev/zero of=/mnt/zero.img bs=1M count=25000 >> 25000+0 records in >> 25000+0 records out >> 26214400000 bytes (26 GB) copied, 245.808 s, 107 MB/s >> >> Directly make filesystem on RAID6 block device composed by 7 disks >> dennis@desktop:~$ sudo dd if=/dev/zero of=/mnt/zero.img bs=1M count=25000 >> 25000+0 records in >> 25000+0 records out >> 26214400000 bytes (26 GB) copied, 129.543 s, 202 MB/s >> >> Thin volume on top of a thin pool created by a Plextor M5P 128GB SSD >> as metadata device >> and a RAID0 block device composed by 7 disks as a data device >> dennis@desktop:~$ sudo dd if=/dev/zero of=/mnt/zero.img bs=1M count=25000 >> 25000+0 records in >> 25000+0 records out >> 26214400000 bytes (26 GB) copied, 46.1227 s, 568 MB/s >> >> Directly make filesystem on RAID6 block device composed by 7 disks >> dennis@desktop:~$ sudo dd if=/dev/zero of=/mnt/zero.img bs=1M count=25000 >> 25000+0 records in >> 25000+0 records out >> 26214400000 bytes (26 GB) copied, 48.1104 s, 545 MB/s >> >> It is clear that the write performance has degraded significantly when >> we use RAID6 as thin-pool, >> but there is no similar behavior when using RAID0 as thin-pool instead. >> I dig a little deeper on this issue and find that if we can perfectly >> fit a pool block into a RAID6 stripe, >> there would be only 20~30% performance loss comparing to RAW RAID6. >> However, this poses a restriction on the disks number we can use to >> build a RAID6 for pool, and limit the maximum pool size as well. >> Is there any other way I can do to improve the write performance when >> using RAID6 as pool? > > > > Since you have not provided any 'dmsetup table' output - it's hard to guess > how your thin-pool target is created, but my guess is - you are using > 'zeroing' for provisioned blocks. > > i.e. here is some sample for thin-pool target line with disabled zeroing: > > vg-pool-tpool: 0 40960 thin-pool 253:1 253:2 128 0 1 skip_block_zeroing > > > (and example of lvm2 command line: 'lvcreate -T -L100G -Zn -c1M vg/pool' > > Zdenek > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
