Customer is experiencing poor Sybase ASE 15 performance on a PS6000X SAN with 16 X 450GB 10K in RAID-50. The server is a Dell R710 running 2003 server R2 64bit in ESX 4.0.0,256968 I've used sqlio to benchmark the sequential write performance of 4KB blocks on the drive. sqlio -kW -t1 -s600 -dE -o1 -fsequential -b4 -BH -LS sqliotestfile.dat Result is 1900 IOPS. However, when Sybase is running a sustained workload of small inserts SAN HQ shows a consistent 590 IOPS (and 100% 4K write activity). It also shows that the write latency increases to 1.2ms from <1ms. Monitoring and tests in Sybase demonstrate the performance problem is IO related and in particular there is a lot of wait time writing to the log. The SAN indicates that write caching is enabled. What IOPS should the SAN be capable of for 4k sequential write activity? Also, with write caching enabled, shouldn't the controller be batching up the 4K writes into something more efficient? Also, any tips on Sybase on ESX would be appreciated.