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Main Question : Would I see any benefit (I/O bandwidth-wise) to purchasing a separate (non-raid) PCI-e controller card to plug SATAII drives into vs on-board SATAII slots?

I'd be plugging at least four drives into whichever solution I go with.

Context :

For portability reasons, I'm running a fileserver in a VM (the physical machine is dedicated explicitly for running this VM), serving files from a number of virtual disks each located on its own physical hard-drive. The host has its own dedicated drive, and the VM is also on its own physical, software-raid-mirrored drive. Occasionally I'll see some slowdowns in the I/O for reading/writing files to/from the server and I'm suspecting the fact that right now all of this is being done over the PCI bus. (Limited to 100Mb/s vs 150Mb/s for SATA).

I was willing to tolerate being limited to 100Mb/s via the PCI bus, but I'm starting to want something faster.

The machine that is running all this is a little old (P4, no PCI-e slot) so I'm considering an upgrade. I'd like whatever solution I end up going with (just a new board with >4 SATAII connections or a new board and a PCI-e controller card with 4 SATAII connections) to have as much bandwidth as possible for the disks, without getting into enterprise-level controller cards etc.

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up vote 2 down vote accepted

No, you won't see any benefit. In fact there might be a very slight performance decrease if you use the PCI-e SATA controller.

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Perfect, thanks! – Peter Bernier Sep 16 '09 at 12:07

Third-party SATA controllers usually are for hardware RAID configurations and people who don't have enough SATA ports on their motherboard. Unless you need the advanced RAID features (or if you have enough ports on your motherboard), don't bother.

When I say "advanced" I don't mean non-standard RAID levels. I just mean that it removes most of the software-related overhead by using RAID (which is even present to some extent with onboard systems).

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