Write Performance double Read Performance
Quoted 14 lines · Terrence Martin
I have the following system(s)
Dual 2.8 Ghz Xeon 2U Supermicro Server with 2GB RAM Qlogic QLA2310f Controller
attached to an...
Infortrend A16F with 16 300GB WD IDE PATA Drives
The array as a RAID 5 Array with 3 partitions of 1.4TB each. I have mounted one of the partitions to test.The OS is....
Quoted 7 lines
Fedora Core 1 with the latest Fedora 2.4 Kernel (2.4.22-1.2174.nptlsmp) I have compiled the QLA drivers from the Qlogic site and am using v6.06.10.
The problem I am noticing is that while doing an IOZone performance test I get nice write performance when the test gets to large files. However
my read performance seems to be a little over half my write. I thought
the read should always be faster than the write?
Unfortunately I don't know why, but this is something I've been thinking of asking as well.
I've seen similar behaviour on a 2.6.3 kernel machine (dual 2.4 Xeons, 2GB RAM) using an external U160 SCSI Chaparral hardware RAID 5 on a aic79xx controller. I'm using XFS on the RAID.
I've just been using 'lmdd' to/from a 2Gb file - I also see writes about twice the speed of reads (I'm using the fsync or sync option to lmdd with the writes).
However, if I increase the readahead on the disk using blockdev from the default of 256 to 4096, I can get read speeds to be about the same as the writes.
However, increasing the readahead seems to help this simple streaming case, but as yet I don't know if it will work in a general file serving (NFS) situation.
Quoted 6 lines
Before I went down the road of compiling various kernels etc I thought I would post this to linux-scsi to see if it is just some configuration setting to a driver or kernel parameter that needs to be tweaked. Of course I could be completely reading this wrong but bonnie++ also appears to give similar results and vmstat is similarly low on the read side.
I would also like to know of any optimizations that can be made.
Thanks
James Pearson