[Linux-cluster] GFS on CentOS 5.2

Shaun Mccullagh Shaun.Mccullagh at espritxb.nl
Mon Dec 8 20:00:02 UTC 2008


A few weeks ago I started to setup a 6 node GFS cluster connected to a SAN with Fiber HBAs. Each node is connected to 2 gigabit switches for redundancy.

Up until a few days ago things were going very well, but intensive testing showed that we have a bit of a performance problem.

Perhaps I should explain that we want to use GFS in a LAMP environment to speed up a customer website.

The old system consisted of six nodes which shared files using glorious NFS.

But we have found to our dismay that Apache is taking much longer to access files via GFS than NFS. Strace shows that the Apache workers are waiting on fstat calls. They take 4 times longer to complete on GFS than NFS

 I have tried the following:

- disabled atime updating: mount option 'noatime'
- disabled quota: mount option 'noquota'
- increased statfs_slots: gfs_tool settune <mountpoint> statfs_slots 128
- enabled statfs_fast (gfs_tool settune <mountpoint> statfs_fast 1)

These improved things slightly but GFS is still much slower than NFS

The CPU load is much higher with GFS, vmstat shows that Context switching is > 5 greater than that of an NFS client.

The GFS filesystem is only 10GB.

We are getting a bit desperate so I'd grateful for any pointers as to what might be going wrong.



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