[CentOS] Performance problem with CentOS and XFS on EMC

We have an appliance that uses the CentOS 4.4 Plus kernel with XFS on an EMC RAID array that performs about ¼ or less as well with cached i/o than with direct i/o.  With direct i/o we get about 32Mb/s throughput or better, but if we enable the cache for the EMC RAID, we only get 8Mb/s or less.  This doesn't happen if we use JFS, where we get a little less than 32Mb/s throughput with or without cache enabled, on the same hardware and CentOS, but there are some features in XFS that we use that are not available in JFS..

 

Any thoughts on this?

 

Thanks.

 

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