Fragmentation Issue We Are Having

[David Fuller <dfuller@xxxxxxxxx>]

We seen to be having an issue whereby our database server

gets to 90% or higher fragmentation.  When it gets to this point 

we would need to remove form production and defrag using the 

xfs_fsr tool.  The server does get a lot of writes and reads.  Is

there something we can do to reduce the fragmentation or could

this be a result of hard disk tweaks we use or mount options?

here is some fo the tweaks we do:

/bin/echo "512" > /sys/block/sda/queue/read_ahead_kb

/bin/echo "10000" > /sys/block/sda/queue/nr_requests

/bin/echo "512" > /sys/block/sdb/queue/read_ahead_kb

/bin/echo "10000" > /sys/block/sdb/queue/nr_requests

/bin/echo "noop" > /sys/block/sda/queue/scheduler

/bin/echo "noop" > /sys/block/sdb/queue/scheduler

Adn here are the mount options on one of our servers:

 xfs     rw,noikeep,allocsize=256M,logbufs=8,sunit=128,swidth=2304 

the sunit and swidth vary on each server based on disk drives.

We do use LVM on the volume where the mysql data is stored

as we need this for snapshotting.  Here is an example of a current state:

xfs_db -c frag -r /dev/mapper/vgmysql-lvmysql

actual 42586, ideal 3134, fragmentation factor 92.64%

Regards,

David Fuller