To Raid Or not to Raid... That is the Question

I have a Gigabyte 8KNXP MoBo that supports IDE Raid and SATA Raid. Currently I have an IDE raid 0 array. I want to go also with a Sata Raid0 array. I have the ICH5r southbridge chip and Silicon Image 3112 chip that both support Sata Raid though the Intel chip supports raid0 only and the other chip supports Raid 0+1. I'm a little confused on which one I should use or exactly how to go about it. Any info would be appreciated...

 

The ICH5r seems to do a good job and its really fast at Post (unlike the Promise onboard chips).

I believe to do RAID 0+1 it would take 4 drives to stripe/mirror.

Do you want to boot from this array? or just and additional storage?

I have 2 RAID zero arrays in my media server.
2 SATA 160s, and 2 IDE 120s.

 

RAID 0. Striping no parity. The data held on the disks is spread across the array in what are called stripes. The system can read and write to more than one disk at once. This makes this the fastest system for read and write. The more disks in the array, the better (performance wise - as long as the bus can support it. So true for SCSI, I'm not sure for IDE - SATA or otherwise).

The down side is that if any disk fails you lose all the data (because the striping information is lost). So the more disks, the more fragile the system. Personally I'd not use RAID 0 for this reason. Hard disks are the most likely component to fail in a PC. Only use RAID 0 if you can live with losing your data (e.g. this may be acceptible on a games system).

RAID 1. Disk mirroring. The data is copied to two disks (RAID 1 works with pairs so only two disks or two matching pairs of disks). Write is slower, because you have to process the writing of data to two disks - the same data is written twice. Read is faster, because you can grab data from either disk (or one bit from one and another bit from the other).

So performance isn't as good as RAID 0, but reliability is greatly improved (not only over RAID 0, but also over a standalone disk). If one disk fails, the other disk will carry on alone. So overall, RAID 1 gives better read speed, superior resiliance, at the cost of decreased write speed and increased complexity over having single disks.

RAID 0+1 Mirrored pair of striped RAID 0 disk arrays. That is you have two RAID 0 disk arrays, each being a copy of the other array. For this you need at least four disks (minimum number of disks in each of the two RAID 0 arrays is 2, and there must be a pair of arrays: 2 * 2 = 4). Often considered the best compromise of RAID 0 performance with RAID 1 resiliance if you only have four disks. A popular solution with high end tape systems.

RAID 5 Striped with striped parity. The other main option used. It's similar to RAID 0 but also includes a disk's worth of parity data. Not room here to go into detail but the effects are: you need an extra disk (so minimum of three disks in the array), if a disk fails the system can use the parity information to rebuild the information on that disk - so the system can survive a disk failure. Performance wise, write is quick (but not as quick as RAID 0 because RAID 5 also has to process and write parity bits), read is almost as quick as RAID 0 (not quite as quick because there is always one less disk to read from). This is probably the best compromise of performance over resiliance. You need at least three disks, but the more the better (for performance). You can also do clever things like have live spares that get automatically built into the array if a disk fails. This is the system favoured for most SCSI servers. It also allows you to build large arrays (a RAID 5 array of six 200Gb disks would give you a 1Tb space [6*200 - 200]).

Personally, on an IDE system I'd suggest RAID 1 is the best option for most circumstances.

 

Thanks for your replies ssmith10pn and ReggieB!

I want the Sata raid0 to be my boot drive as it will have the fastest drives (twin 74Gig WD Raptors). According to my manual, ICH5r supports raid0 only and that is fine. It has two ports. Then that leaves two ports on the Sil3112 chipset which supports raid0, raid1 and hot swapping. Too bad I couldn't (later, down the road) mirror the ICH5r raid0 drives with the Sil3112 chipset and a couple more Raptors (I may have to get a direct line in from the hydro pole for power... ).

I think I may do away with the IDE raid for a while as I suspect one of the drives is acting up occassionaly and this would give me a chance to pinpoint which one. Every once in a while I have to run CHKDSK on my array to correct errors. The odd time I actually lose system files and have to do a repair through setup. I know what your thinking ReggieB!
I haven't seen any utilities that will check and diagnose hard drives while they are in an array...

Do you think I could run out of resources (IRQ's, DMA's ....)?

 

Here ya go

9500S-12 Upto 12 Serial ATA 0,1,10,5, 50, Single Disk (JBOD) Security and Surveillance,

Super Computing,
Video On-Demand,
NAS Storage,
Disk-to-Disk Backup


http://www.3ware.com/products/serial_ata9000.asp

 

Isn't that a peice of hardware... A little out of my league I think... although-wait- now you got me thinking ...