# Will a 64-bit RAID card in a 32-bit PCI slot make me cry later, even though it works now?

One of our less-critical servers seems to have lost the use of its onboard SATA controller -- which was managing the software-mirrored boot volume.

The simplest and cheapest fix was to buy a 2-port SATA controller at the local Fry's -- or so it seemed when I was standing in the controller aisle there.

Turns out I bought a 64-bit card, though (a 3Ware 8006-2LP to be precise) -- and the only relevant slots that are free on the server are old-school 32-bit PCI slots.

Am I in for trouble? Just to be clear, I know this will work -- in fact, I've already got it up and running -- and I know it's not a theoretically optimal configuration. What I'm asking is: Will it work well enough for my needs, as outlined below, or will it cause me misery in the long run?

The card will simply be managing 2 mirrored SATA drives, which together act as the server's boot volume. The server itself provides backup and archive storage, acts as a secondary DC, and does a few other things that are important but not day-to-day critical. All of the storage that it exposes to the network is on a separate controller card that's in a PCIe slot.

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I've rephrased the title and reworded the question a bit to make clear what I'm asking -- I guess the original wording made it sound like I was asking if this would work. –  Ben Dunlap Aug 16 '09 at 2:12

A lot of those 64bit PCI cards can be used with 32bit slots. It will plug right in and the last portion of the card will not be used in the slot. Performance wise, you are at the limits of your pci bus. I am not sure how much of performance effect there would be, but I know it will most likely work. The card will sometimes say backwards compatible with 32bit slots.

Here is throughput comparisons of pci 32/64bit 33/66mhz slots.

http://www.compute-aid.com/64bitpci.html

Performance wise, there are many factors. How many other devices are on the PCI bus? They are all sharing the pci throughput potential. Are you using 33mhz or 66mhz 32bit pci slots? The server motherboard specs should say.

EDIT:

You stated that you got it up and going already. That is good to hear. Do you notice any significant slowdowns or performance issues so far? Do your backups and routines finish in the same amount of time as before? If you do not notice any new issues, I would say you are doing alright.

The other factor to consider is this is about your only option for getting that server up and running with sata drives without replacing the motherboard or replacing the server. If you are not seeing anything out of the ordinary, I would say consider this a good solution until server replacement time comes.

I assume the server does not have E-Sata ports on the motherboard?

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It definitely works -- wasn't really worried that it wouldn't. I'm looking more to find out whether there will be any practical negative impact in my environment. My vague sense is that the raw PCI throughput numbers don't tell the whole story and that RAID complicates things even more. But maybe it's simpler than that? –  Ben Dunlap Aug 16 '09 at 1:26
You are correct, there is overhead involved and it depends on what other devices are on the pci bus. I added a couple questions to my answer. –  Troggy Aug 16 '09 at 3:24
No problems so far -- that I've noticed, at least. Backups that read from those disks are completing in normal-looking times. And yes, this was definitely the least painful of all the options I could think of. Seems good so far! –  Ben Dunlap Aug 17 '09 at 23:57
Nope, no onboard E-SATA. This isn't even "server-grade" hardware -- ssh, don't tell the hardware vendor! –  Ben Dunlap Aug 17 '09 at 23:57
Yah, if you are not seeing increased backup times or other performance anamolies, sounds like you have a successful "fix/patch" until next replacement time. Hope that information was useful to you. –  Troggy Aug 18 '09 at 15:57

I have been running a HW raid PCIX card in a "regular" 32 bit PCI slot for a could years.

Like the folks above said, the only downside is speed.

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Should have read, "I have been running a HW raid PCIX card in a "regular" 32 bit PCI slot for a couple years. –  mr.zog Oct 21 '09 at 16:17

The only theoretical problem is bandwidth. 32-Bit/33 MHz PCI has a theoretical 133 MB/s transfer rate, but that is for the complete PCI Bus. Depending on the mainboard, there may be other things running on the PCI Bus as well, for example the OnBoard Network Card (highly unlikely in any modern PC, but some cheaper mainboards still did that until recently) or the OnBoard Graphic Card if it's non integrated into the chipset (i.e. many older mainboards use an ATI Rage IIc or similar PCI Card soldered on the mainboard), but that's also rather unlikely with modern mainboards.

In Short: You're fine, PCI is specifically backwards compatible and using a 64-Bit PCI Card in a 32-Bit PCI Slot is common ever since the first 160 MB/s SCSI Controllers launched 10 or so years ago.

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Yes you can -- in this instance, but not always.

The 3Ware 8000 series will run at a degraded speed on a 32bit PCI port (but no more than any other 32bit PCI adapter...). Newer 9000 series require a 3.3v bus, and are physically notched to not fit in the PCI port.

If for some reason the card wont fit into the port -- dont force it -- return it.

On a side note -- If you are running software raid -- why blow $150 on a hardware raid card when you can pickup a software raid card (sata interface) for$50 or less?

Update

What I'm asking is: Will it work well enough for my needs, as outlined below, or will it cause me misery in the long run?

It will be absolutely fine -- no slower than any other 32bit PCI card. I think short of 4 drives in a raid10 array you would be hard pressed to find a difference except under a pure cache read/write scenario.

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It only ran me $120 after tax and the next-cheapest card was about$20, as I recall, which just seemed a little too low for my comfort. This isn't a "critical" server in the sense that if it goes down all operations cease, but it's still a production server. Plus I'd like the option to convert to hardware RAID in the future. –  Ben Dunlap Aug 16 '09 at 2:03

I've got a similar situation with a SCSI card in an older system. It has a pair of 15k drives on it. It works very well, even though it is limited to about 90 MB/s.

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