Given the choice, would you choose RAID 5 or RAID 10
We are looking to build our first server, and collocate it. It will be a higher investment than just renting the server, but will be worth it in the long term, and we have already decided we are going to support the hosting business for a minimum of 3 years - so we might as well invest in a server from the outset to benefit from lower data center charges and higher redundancy and performance.
We are currently looking at Supermicro for servers as they offer 1U barebones systems with dual hotswappable psus and upto 4 hotswappable drives. This would be ideal for redundancy, and also for taking advantage of the speed and redundancy that a RAID 10 array would give you. These two factors combined are very appealing as it would reduce the possibilities of downtime and data loss. Obviously we will be backing up daily, but its good for piece of mind to know that you could potentially blow a PSU and 2 hard drives, and your server will still be up long enough for a data centre technician to replace the parts.
Now then, my business partner and I are currently deciding what the best all round hard drive configuration would be. He has decided that we should opt for SAS instead of SATA to have lower latency seek times, which would give us better performance. I agree, though this does increase costs considerably.
He is then arguing that we use RAID 5 on cost grounds. He says we should only use 3 of the slots to begin with, save money on one drive by not having a spare, and hope we don't have a drive failure - which sods law will happen. I'm not happy us cutting corners to save money, because if we gamble and lose, that's a hell of a mess we have ourselves in, and will cost us a load more time, reputation and data center charges to get ourselves out of it.
I say we might as well go for RAID 10 for that extra performance, and redundancy, you can potentially lose 2 drives so long as they aren't from the same mirrored pair. With RAID 5 you can only lose a drive, it takes longer to rebuild onto a spare, and during rebuild the performance takes a hit. Also RAID 10 is much faster than RAID 5, and at the expense of the cost of a drive.
Now the question we should be asking is... would a SATA2 RAID 10 array provide better performance than a SAS RAID 5 array?
So I think the choice we have to make is either go for RAID 5 and run with a hot spare, and stock a cold spare, or go with RAID 10 and stock 2 cold spares.
We are considering going with Seagate drives because they are high performance and have 5 year warranties. I have had to RMA two Western Digital drives already in the past 12 months, a raptor and a mybook, both deaths invoked data loss.
PS. The server is going to be a linux web, email, dns and mysql box. It will likely feature a single dual/quad core processor, and 4-8GB of unbuffered ddr2 ram.
In my experience, I think you'll find 4 SATA2 drives in a RAID10 (to avoid confusion, 2 seperate sets of data striped over 2 drives, for a total of 4 drives) array will provide you the best seek times, especially in a database heavy environment (read: lots of random seeking, pardon the term seeking). It will also be more cost effective than SAS drives in a RAID 5 array. And the saved money can be invested in a quad core CPU (make sure it has the cache to take full advantage of the extra two cores) and extra ram (I figure it's common sense, but make sure it's ECC). To be honest though, I would seperate the database from the web/email/dns services. A setup with a dual core box with RAID0 (2 SATA2 drives) and a large extra drive to maintain a backup of the database to run the web/email/dns services coupled with a quad core box with ~double the ram and 4 SATA2 drives with the aforesaid drive configuration (and an extra copy of the web data, extremely large files absent to not waste space) to run the database server would be the most cost effective, especially in the added redundancy and scalability for the future -- rather than having to take your sites offline, you can simply run all services from one box at off hours while upgrading the other box. Adding to the cost effectiveness, you will not need to upgrade either for quite some time, and the added redundancy will no doubt pay off when the unthinkable happens. Although there will be a higher initial cost, I find it difficult to justify downtime to save a relatively small amount of money (I'm guessing that you business plan has server costs as a much smaller proportion compared to HR costs. And from the gist of your post, you prefer reliability and efficiency over saving ~$400 off the bat).
SAS is going to be faster either way. Unless you are going to have heavy disk I/O, I would stick with sata raid5 with a hot spare or sata in raid10. SAS would get you better performance but at a higher cost.
If you're quibbling over the cost of a 4th hard disk you really shouldn't be buying servers / colocating, but anyway...
From memory 4xSATA in RAID10 will get you around 75MB/s read, 3x10K SAS in RAID5 will get you ~ 100MB/s read. Obviously your bottleneck with RAID5 is slow writes, if your database usage is going to be quite heavy you'll have problems with RAID5.
I'd go with the SAS RAID5 option, preferably with a hot spare, providing database activity is not the server's primary function. Providing the controller supports it you could also potentially go for a 4xSAS in RAID6 configuration which works much better than 3xRAID5 plus hot spare (your 4th disk is actually being used rather than sitting idle) and it doesn't have to rebuild since the data is already there (double parity).
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RAID6 is dual parity. You used 4 drives, but two drives will be used for parity. Performance wise, it should be similar, if not slower, to RAID5.
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RAID10 with 4 disks with outperform RAID5 with 3 disks 2 to 1 on average with the same disks. You save 25% in storage costs and lose 50% in perfomance. So you do the math which is the most important to you.