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SATA or SCSI - need advice

Posted on 2006-05-15
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Hi, I need some advice from little experienced experts.
I'm about to buy a server, which would be application server for about 20 xterminals.
Nothing sophisticated. No development. Web browsing email reading possibly document writing.
Runnig under linux.

Now, what would You suggest as a storage?
I was thinking about 3ware or ich7 (NCQ) + 2 150G SATA Raptors in mirror (either software or hardware from 3ware)
As opposite I could use smaller SCSI disks with linux software mirror.

What You think? Maybe some links to some comparation tests?
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Question by:ravenpl
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rindi earned 1000 total points
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If you go for SATA, take 3ware or Areca controllers, not the ich, and go for hardware and not software. The raptor is a good SATA drive and it should be OK for your system. Of course if you have enough $$$'s to spare, SCSI is the better choice, but you can easily get an extra SATA HD and it will still cost less than SCSI with 2, so if your HD's crash it is easier to afford changing them.
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by:rindi
ID: 16680936
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by:ravenpl
ID: 16681016
Thanks for the  Areca link - I wasn't aware of such controller, I thought that the world starts and ends at 3ware ;)

Why You so strongly against software mirror? It looks good, no resources usage, read dispercing. If the driver and controller and drive would support NCQ, should work well.
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by:rindi
ID: 16681080
It still uses the PC's CPU. Of course with mere mirroring (if you don't need a higher level of raid like raid5 etc) that isn't a big deal. Software raid controllers are often not well supported in linux and need some tweaking, you often have to use software raid inside linux itself to get them going. For hardware raid it is more likely you have direct linux support, also because the cards are more expensive they have to supply better support.
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by:garycase
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ID: 16683039
"... the world starts and ends at 3ware ..." ==> It does :-)  ... for high-end RAID-5 capable controllers with in-place array expansion and other sophisticated control/management capabilties.

However ... for what you've proposed there is NO performance advantage with 3ware.   The ICH7 chipset is an excellent built-in RAID controller; and is NOT a "software RAID" => the array management features are controlled via software (in the BIOS), just as with 3ware, Areca, etc.; but the I/O management is built in to the ICH7 controller.   The ICH7 does NOT include more sophisticated functions - notably hardware XOR capabilities that are needed to implement RAID 5, 50, etc. => but for an array that doesn't require these (e.g. RAID 1) there's no real downside to it; and the upside is that if you're using a PC with a PCI bus (vs PCI-e) you aren't limited to the PCI data rate (although with RAID 1 that's not a bottleneck).   The more sophisticated controllers (e.g. 3ware) do allow in-place array expansion -- a very nice feature if you ever need to expand your array -- but in reality most of us will completely backup the array before doing such a thing anyway ==> and backing up; deleting/recreating the array; and then restoring is usually a faster process than waiting for a pair of larger drives to (one at a time) be restored and then doing the in-place expansion.  (of course the latter can be done with no down-time)

... back to your question:  "SATA vs SCSI" ==>  Modern SATA drives - particularly an enterprise-quality drive like the Raptor's - are extremely reliable.   SCSI drives ARE built to more demanding specifications, and have even better performance capabilities (15,000 rpm vs 10,000 rpm; 3.9ms avg seek vs 4.6ms for a Raptor), but there's a significant price premium for this relatively marginal gain in performance and reliability.   For the application you've described, a pair of high-quality SCSI drives would be fine.   ... and if you want to improve your performance, I'd go with 4 Raptor's on an ICH7 controller in RAID-10.   That would cost appreciably less than a 2-drive SCSI system;  have much more capacity; and outperform it in data transfer rate (but not in seek time).
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by:rindi
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I don't think the ICH7 has any proper linux support.
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by:garycase
ID: 16683529
... I don't know the answer to that ==> but the Fedora Core installation guide clearly indicates that if motherboard-supported RAID is configured, it will use it just fine.   Haven't tried it with Linux, so I don't know.   Worth a try I'd think.
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by:ravenpl
ID: 16683624
ich7 is supported by the ahci driver under new linux kernels. That's OK.
But garycase: so far I know linux sees physical drives instead of array configured with ich7's bios...
There is driver provided by intel, but people say to use linux soft raid instead.
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by:garycase
ID: 16684145
The kernel may only be using the ich7 in "IDE" mode - in which case the array won't be seen.  The only reason I can think of to use Linux soft-RAID instead of the ich7 is if you want to use a RAID mode not supported by the ich7 -- unless there's some conflict with the Intel driver.

But either should work fine -- the disadvantage of the software approach is primarily the CPU overhead; and for a mirrored array that won't be too bad.    I'd suggest trying it with the ich7 driver first, however => the CPU overhead for the Intel driver is typically < 1%
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by:scrathcyboy
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I would use a mirror for sure, either RAID 1 or RAID 10 (if you want 4 drives) -- sure a mirror is somewhat slower, but with modern fast drives, you wont notice much difference, and with a mirror, you will never lose your data.  People are always losing RAID 0 and 5 arrays, evidenced by number of problems coming in to EE.
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by:ravenpl
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Thank You.
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by:rindi
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your welcome
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by:garycase
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You're most welcome.
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