Re: Slow write times to gluster disk

[Ravishankar N <ravishankar@xxxxxxxxxx>]

Hi Pat,

I'm assuming you are using gluster native (fuse mount). If it helps, you could try mounting it via gluster NFS (gnfs) and then see if there is an improvement in speed. Fuse mounts are slower than gnfs mounts but you get the benefit of avoiding a single point of failure. Unlike fuse mounts, if the gluster node containing the gnfs server goes down, all mounts done using that node will fail). For fuse mounts, you could try tweaking the write-behind xlator settings to see if it helps. See the performance.write-behind and performance.write-behind-window-size options in `gluster volume set help`. Of course, even for gnfs mounts, you can achieve fail-over by using CTDB.

Thanks,
Ravi

On 04/08/2017 12:07 AM, Pat Haley wrote:

Hi,

We noticed a dramatic slowness when writing to a gluster disk when compared to writing to an NFS disk. Specifically when using dd (data duplicator) to write a 4.3 GB file of zeros:

• on NFS disk (/home): 9.5 Gb/s
• on gluster disk (/gdata): 508 Mb/s
  

The gluser disk is 2 bricks joined together, no replication or anything else. The hardware is (literally) the same:

• one server with 70 hard disks  and a hardware RAID card.
• 4 disks in a RAID-6 group (the NFS disk)
• 32 disks in a RAID-6 group (the max allowed by the card, /mnt/brick1)
• 32 disks in another RAID-6 group (/mnt/brick2)
• 2 hot spare
  

Some additional information and more tests results (after changing the log level):

glusterfs 3.7.11 built on Apr 27 2016 14:09:22
CentOS release 6.8 (Final)
RAID bus controller: LSI Logic / Symbios Logic MegaRAID SAS-3 3108 [Invader] (rev 02)



Create the file to /gdata (gluster)
[root@mseas-data2 gdata]# dd if=/dev/zero of=/gdata/zero1 bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 1.91876 s, 546 MB/s

Create the file to /home (ext4)
[root@mseas-data2 gdata]# dd if=/dev/zero of=/home/zero1 bs=1M count=1000
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 0.686021 s, 1.5 GB/s - 3 times as fast


Copy from /gdata to /gdata (gluster to gluster)
[root@mseas-data2 gdata]# dd if=/gdata/zero1 of=/gdata/zero2
2048000+0 records in
2048000+0 records out
1048576000 bytes (1.0 GB) copied, 101.052 s, 10.4 MB/s - realllyyy slooowww


Copy from /gdata to /gdata 2nd time (gluster to gluster)
[root@mseas-data2 gdata]# dd if=/gdata/zero1 of=/gdata/zero2
2048000+0 records in
2048000+0 records out
1048576000 bytes (1.0 GB) copied, 92.4904 s, 11.3 MB/s - realllyyy slooowww again



Copy from /home to /home (ext4 to ext4)
[root@mseas-data2 gdata]# dd if=/home/zero1 of=/home/zero2
2048000+0 records in
2048000+0 records out
1048576000 bytes (1.0 GB) copied, 3.53263 s, 297 MB/s 30 times as fast


Copy from /home to /home (ext4 to ext4)
[root@mseas-data2 gdata]# dd if=/home/zero1 of=/home/zero3
2048000+0 records in
2048000+0 records out
1048576000 bytes (1.0 GB) copied, 4.1737 s, 251 MB/s - 30 times as fast


As a test, can we copy data directly to the xfs mountpoint (/mnt/brick1) and bypass gluster?


Any help you could give us would be appreciated.

Thanks

-- 

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Pat Haley                          Email:  phaley@xxxxxxx
Center for Ocean Engineering       Phone:  (617) 253-6824
Dept. of Mechanical Engineering    Fax:    (617) 253-8125
MIT, Room 5-213                    http://web.mit.edu/phaley/www/
77 Massachusetts Avenue
Cambridge, MA  02139-4301

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