Simon Banton wrote: > At 11:16 -0400 14/9/07, Ross S. W. Walker wrote: >> Yes, a write-back cache with a BBU will definitely help, also your >> config, > > The write-cache is enabled, but what I've not known up to now is that > the absence of a BBU will impact IO performance in this way - which > seems to be what you and Feizhou are saying. Is there any way to tell > the card to forget about not having a BBU and behave as if it did? Short of modifying the code...I do not know of any. > > The main problem here is the latency when under IO load not the > throughput (or lack of). I don't care if it can't achieve 300MB/s > sustained write speeds, only that it shouldn't bring the machine to its > knees in the process of getting 35MB/s. SATA 7200RPM disks are not exactly fantastic at random i/o. The cache only boosts writes in a significant way and less so for reads. Maybe you could consider RAID10. That way, them 7200RPM disks are a match if not better than hardware raid with BBU cache for a mirror of scsi drives.