Higher writes on XFS filesystem via LVM than expected

Florian Jauernig fjauernig at gmx.de
Wed Sep 1 08:17:17 CDT 2010


Hi List,

hopefully this list is a correct place to ask...

I am facing a strange problem with my NFS server: although network interface 
statistics only show up about 21Mbit/s incoming traffic, I am observing 
about 110 Mbit/s writes to my storage with iostat.

With iotop I can see, that the nfsd processes only use some thousand kbit/s. 
But total disk writes per second are about 110Mbit/s reported by iotop are 
again about 110 Mbit/s.

I have to mention that I am no storage expert, but I tried my best with 
searching for best practises in the internet of how to configure my setup.

My configuration:

We have a good old Poweredge 1850 acting as a NFS server for 3 VMware ESX 
servers (Poweredge R510).

As storage I have an EMC CX300 with 2 LUN's. Each of the LUN's is a RAID 10 
of 10 disks. The storage is directly connected (no switch, etc). Each LUN is 
owned by another Storage Processor. We have multipathd running so in case a 
fibre link is going down we have failover.

I created one big volume with LVM that consists of these 2 LUN's.

As filesystem I am using XFS.

I tried my best so everything is aligned (Partitions accordingly to the 
stripe size of the LUN's), Metadata of the LVM PV's is hopefully also 
aligned.

XFS is hopefully correctly tuned with sunit and swidth, and mounted with 
relatime and nobarrier.

On kernel level I am using noop scheduler (so the CX300 storage processors 
can do the scheduling work and do not interfere with each other).

Has anyone an idea what might cause the much higher constant writes to disk 
than expected by NFS? If you need further information like exact 
configuration or logfiles I will append those.

Any help is greatly appreciated!

Thanks in advance

Florian
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