[Gluster-users] Slow write times to gluster disk

[Ravishankar N]

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