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SCSI vs. SATA In a File Server?
turboflux asks: "I'm currently in the process of replacing an aging file server with something more robust. Company-wide, there will be about 100 people who could be using this server, but I don't imagine there being more than 50 concurrent users. Right now, I'm torn between spending alot on SCSI hardware, much like our other servers, or spending less, but getting more space, with SATA II drives. Whatever I decide, the server will be setup with a RAID 1+0 array for the numerous benefits it offers. Does Slashdot have opinions or suggestions on performance, reliability, and stability?"
Think about the fact that you need a sufficient Backup. You can buy lots of cheap storage with SATA Disks, but Ultrium 3 Tapes (400/800) are still expensive as fuck. Never forget that cost when calculating.
OTOH, there are 300GB U320 Disks now, which you could use if latency is not an issue. Otherwise, go with lots of disk arms (72GB or 36GB U320 Disks)
SAS hardware is currently a little harder to find than SCSI or SATA stuff, but I'm sure there's a good selection out there if you take the time to look.
I was checking out the Sun Fire 4100 a while ago, and it takes SAS drives, however the form factor is 2.5", and I haven't yet seen any 2.5" SATA drives (I wanted that compatibility). Also, I've heard SATA drives don't work with the Sun Fire 4100's SAS controller anyway. Not sure about that, since the SAS spec says they should work, but just something to keep in mind when you're looking for a server or mobo or controller that supports SAS.
OK, hear mine then.
We have several terabytes of SATA storage at work to hold our main business-critical digital asset archive.
We've been using a ATA/SATA disk-only strategy for over 5 years now. It's worked great, and eliminated our slow and unreliable tape robot, which has greatly improved productivity.
Back in 1999/2000 SCSI wasn't an option for the main archive because a terabyte of SCSI would have broken the bank. We went ATA back then. It was a mess trying to route 24 ATA cables in a case, I admit. SATA fixes that nicely.
We keep three copies of our data, two onsite and one offsite. We use rsync-incremental snapshots to do disk-based incremental backups. Because the cost of SATA is less than 1/3rd the cost of SCSI, we get a high reliability solution for less than the price of a single SCSI RAID.
One more advantage of SATA is that the disks are so cheap, it's easy to just replace all of them every two or three years. The disks you replace them with generally are twice as large after 2 or 3 years, so every cycle your RAIDs get more reliable as the number of disks is slashed in half.
Most companies wouldn't replace every SCSI disk every two years, it would cost way too much. And considering the slow pace of SCSI size growth, you wouldn't see as much gain, a double hit against SCSI.
So basically unless you need the excellent latency performance of SCSI, higher than even the WD Raptor can offer, I see no compelling reason to use SCSI for anything anymore.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
Some more tips for you:
First, make sure you get a SATA2 controller. NCQ is a must for multiuser environments.
Second, whatever controller you buy, grab 3 of them. RAID is great for disk failure, but people rarely think about what they'll do when the controller fails.
Look at some of the stranger RAID options. If you just use RAID5, you'll be selling yourself short. RAID3 is worth a look. I'd actually suggest you put two controllers in a machine. Run RAID0 on 4 drives on a single controller. Run RAID0 on 4 drives on the other controller. Then use Windows or Linux software RAID to run RAID1 between the two RAID0 drives. Very fast performance and fully fault tollerant.
Keep the OS on a small, slow hard drive seperate from the array. You can do funny things there, but I'd suggest you set it up properly and then use a disk clone utility to create an offline backup to store somewhere.
Arrange for testing in the first few months. Unplug drives from the array and see what happens. Verify that you can restore from tape backup to the array. Veryfy that your cloned OS hard drive can actually get the array online. Extensive testing before you go live. Two tests in the first month after going live. One test every 6 months after that.
If you are using commodity servers, get a spare for everything in there.
If you want high avalibility, look into DRBD. It's like RAID1 over a network.
Monitor the damn thing! My last job someone let the server die. It had RAID5 over 5 drives. One drive had failed and no one noticed. When the second failed, that was the end of it. Learn to use SNMP or get some good monitoring utilities that will notify you of problems. You need to know if a drive fails, if it reports SMART errors, drive temp, proc temp and usage, NIC utilization, drive utilization, system temp, and memory utilization. MRTG+RRD Tool and SNMP will give you pretty charts for all that crap. MotherboardMonitor will also give some nice readouts for Windows. If it's commodity server, look at installing a Crystalfontz LCD so that you can walk by and get a quick status without the need to login.
I'd rather you do it wrong, than for me to have to do it at all.