I was rather disappointed with the results. Can anyone suggest what might be causing such slow disk speeds, or whether these speeds are out of the ordinary for a 4-disk FreeBSD RAID5 installation? I have done nothing to configure the card aside from striping the array in BIOS; FreeBSD seems to automatically detect the disks.
For us to be able to comment beyond generalizations, it's necessary to also benchmark how a single disk performs. I can still answer your question, though:
RAID-5 is slow. RAID-5 trades availability against performance and hardware costs. With RAID-0, n drives gives n drives' worth of usable space. With RAID-5, n drives gives n-1 drives' worth of usable space. The performance is between RAID-0 and RAID-1 is comparible for large accesses. For small accesses, particularly small writes, RAID-5 performance is much worse than plain RAID-0 or a plain disk.
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