Topic: RAID
started by: Tattered
Posted by Tattered on Jan. 25 2002,22:23
I've been hearing a lot of HDD's in a RAID setup, anyone know the benefits of this? (mm.. i need some juicy details) nice.. I just noticed that I kept my posts from the old board.
Posted by Rshias on Jan. 25 2002,23:10
RAID provides a method of accessing multiple individual disks as if they were one large disk. To do this, it spreads data across the disks, thereby reducing the risk of losing all data if one drive fails, and improving access times/transfer rates.The most common setup you'll see outside of the workplace is RAID-0. This isn't "true" RAID by the definition, because it doesn't improve the fault tolerance of the disks. However, what it does do is improve overall disk transfer rate. This is extremely noticeable if you find yourself frequently accessing large files. This is what most home users use in their RAID capable machines.
Below are the descriptions of each setup as ripped directly from the manual:
RAID 0: Also known as "Disk Striping". Data is written in blocks across multiple drives, so one drive can be writing or reading a block while the next is seeking the next block. The advantages of striping are the higher access rate, and full utilization of the array capacity. The disadvantage is there is no fault tolerance - if one drive fails, the entire contents of the array become inaccessible.
RAID 1: Known as "Disk Mirroring" provides redundancy by writing twice - once to each drive. If one drive fails, the other contains an exact duplicate of the data and the RAID can switch to using the mirror drive with no lapse in user accessibility. The disadvantages of mirroring are no improvement in data access speed, and higher cost, since twice the number of drives is required. However, it provides the best protection of data since the array management software will simply direct all application requests to the surviving disk members when a member of disk fails.
RAID 3: RAID level 3 stripes data across multiple drives, with an additional drive dedicated to parity, for error correction/recovery.
RAID 5: RAID level 5 is the most popular configuration, providing striping as well as parity for error recovery. In RAID 5, the parity block is distributed among the drives of array, giving a more balanced access load across the drives. The parity information is used to recovery data if one drive fails, and is the reason this method is the most popular. The disadvantage is a relatively slow write cycle (2 reads and 2 writes are required for each block written). The array capacity is N-1, with a minimum of 3 drives required.
RAID 0+1: This is stripping and mirroring combined, without parity. The advantages are fast data access (like RAID 0), and single ¡V drive fault tolerance (like RAID 1). RAID 0+1 still requires twice the number of disks (like RAID 1).
If I missed anything, someone kick me.
Posted by Tattered on Jan. 26 2002,06:49
So, .. I've got 2 hard drives at home, if I wanted to set them up in RAID-0 (to get some extra speed) what would I need?
Posted by damien_s_lucifer on Jan. 26 2002,09:59
| Quote (Tattered @ Jan. 25 2002,22:49) |
| So, .. I've got 2 hard drives at home, if I wanted to set them up in RAID-0 (to get some extra speed) what would I need? |
You'd need a RAID controller card, such as the Promise Fastrack.
BE FOREWARNED... RAID 0 has *NO* data recovery mechanism. This means if one drive in the array fails, you lose EVERYTHING IN THE ARRAY. HDD's fail all the time, and with RAID 0 you're doubling your risk. Don't store the data you love on it
Posted by Rshias on Jan. 26 2002,17:54
Seek times are especially important in RAID-0 setups because neither drive begins transfering until they both find the information. Try to make sure both drives have identical seek times or you're just wasting performance.Usually just having two identical drives is the easiest solution, this way you get the full benefits of the RAID. In your case, where you have a couple spare drives laying around, you'll still get a performance boost even if the drives aren't the same. This boost will come in the form of increased transfer rates. If the seek times are different, you're going to slow down overall access time though. In a situation like this, it's really not worth going to a RAID setup unless you frequently access extremely large files. For normal useage, you'll just slow yourself down.
Be sure the drives are a quality brand. Just like damien said, you're doubling your risk of a drive failing in a setup like this. A third drive is usually nice to have for backups.
Posted by CNCJake on Jan. 28 2002,18:00
if you dont need any cdrom drives, you can just use software raid in Win2K by using both both ide channels of your mobo.
Posted by MattimeoZ80 on Feb. 06 2002,04:21
i'd definitely suggest buying a controller, even if it isn't a true hardware controller (the promise fasttrak series is an example of this). you really don't want to rely on win2k for raiding, with a card you can still access your drives in any os and use any filesystem. this is useful if you have a corrupted file and need to go fix something; if its win2k software you'd lose everything. i've had no problem with my fasttrak100 tx2, and the speed boost is quite amazing (of course you need a decent system to notice any difference, and a 66mhz pci slot helps if you have good hard drives). raid is definitely worth it if you are willing to increase your risk of failure 2x (2 drives have twice the chance of screwing up, or statistically they'll screw up 2 times sooner than 1).