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Why RAID?
With a RAID you can choose if you want your drives to be very fast, very safe, or a combination of the two. RAID 0 is the fastest, RAID 1 is the safest, and RAID 5 is a great combination of safe and fast. Keep reading to learn what the different RAID levels mean.
WiebeTech's most poupular RAID product line, RTX, are easily configured into many advanced RAID types - including RAID 5 which is widely regarded as the optimal level for both speed and data safety. If a disk goes bad in an RTX (it's a fact of life that all drives eventually fail), an alarm alerts you, telling you to put in a new hard disk for a rebuild of the data.
What is RAID?
RAID stands for Redundant Array of Independent Disks.
RAID, basically, is a form of data management for more than one physical disk. That is, how your data is stored and where your data is stored.
Very simply put, RAIDs will allow you to treat multiple hard drives as a single volume on your computer.
How it treats them depends on the "RAID level" - You'll have to pick the RAID level that makes the most sense for your needs.
What are the RAID levels?
RAID 0 (striping):
This will "stripe" two or more hard drives together and treat them as one large volume. For example, two 250GB drives will RAID 0 to a single 500GB volume. Ten 250GB drives would show up on the desktop as a single volume with 2.5 terabytes of storage.
Advantage: Because a little of the data written is kept on each drive, performance of the stripe increases the more disks are added to it. Writing to 10 drives is roughly 10 times faster than writing to 1 drive. This is especially handy if you need large and fast volumes.
Disadvantage: Every drive has a limited life and each disk added adds another point of failure to the RAID. Every disk in a RAID 0 is critcal - losing any one of them means the entire RAID (and all of the data) is lost.
Despite the disadvantage, RAID 0 is used by those wanting the most performance out of two or more drives. Video/Audio editors commonly use RAID 0.
RAID 1 (mirroring):
RAID 1 will create an exact duplicate of a volume on the fly. Every time you write information to one drive, the exact same information will be written to the other drive(s) in your mirror.
Advantage: This is the most safe option for your data. If one drive is lost, your data still exists in its complete form, and will take no time to recover.
Disadvantage: It doubles cost since you now have two drives but use them as one.
Use: Set up the mirror and operate like normal. Some people will take one of the mirrored drives off site every night and allow the mirror to build on a third drive. If at any point a mirrored drive fails, there is no down time, as the data still exists in full on a backup drive. Important files (accounting, financial, personal records) are commonly backed up with a RAID 1 solution.
RAID 2:
A rare implementation of striping similar to RAID 0 - it stripes at the bit level instead of by blocks.
RAID 3:
An implementation of parity striping. Its limitation is that it cannot service multiple requests.
RAID 4:
Parity striping at the block level with an entire disk dedicated to parity data. Similar to but less common than RAID 5.
RAID 5 (parity striping):
A common RAID setup for volumes that are larger, faster, and more safe than any single hard drive.
Parity striping at the block level with user data and parity data striped across all disks.
At least three disks are required for RAID 5. No matter how many disks used, an amount equal to one of them will be used for the parity data and cannot be used for user data.
Parity data, quite simply, is the result of a quick equation.
Here's a simple way to think of parity:
6 + 3 = 9
Imagine the 6 on one hard drive, the 3 on another, and the 9 on a third.
The 3 and the 6 are your data, but the 9 is the result of a simple equation. If a hard drive were to fail, and you lost, for example, the 3, you could do a simple calculation to retrieve the 3 (9 minus 6).
In a RAID 5, you can lose any one disk and expect to safely restore the data on it after you replace it.
RAID 6:
RAID 6 is very similar to RAID 5 - but it adds an additional parity block. It allows for the failure of two disks simultaneously with no data loss.
RAID 6 is slightly slower than RAID 5 on writes (due to the extra calculation of the added parity block), but there is no added delay for reads.
RAID 0+1 (mirror of stripes) 10, 30, 50 and 60::
These are nested RAID levels - now, instead of RAIDing many single drives, you're RAIDing RAIDs made up of drives.
0+1: Mirror (RAID 1) of two stripes (RAID 0). First, disks are striped together, and then those disks are mirrored to two more disks.
10: Stripe of two mirrors (RAID 1s).
30: Stripe of two RAID 3s.
50: Stripe of two RAID 5s.
60: Stripe of two RAID 6s.
What's the difference between striping and spanning?
Striping and spanning are both forms of RAID 0.
In a stripe RAID setup, the RAID will write a little bit of data to each drive in turn. The cool part is that it can write to all disks in the RAID at the same time. Because of this a user will see a speed increase for every drive added to the stripe.
Spanning, on the other hand, will write to one disk until it is full and then begin on the next disk. Someone might choose spanning if they have hard disks of different sizes but for some reason would like to treat them as one volume.
How can I RAID?
At the very least you need two hard drives and a way to RAID them. Mac OS X has built-in software to RAID 0 or RAID 1 drives together, and commercial RAID software is available for Mac OS or Windows.
Some RAID levels require at least 3 disks, but some only start making sense if you use 4 or 5. You'll want to buy matching drives for your RAID, so a little thought is needed when selecting your drives.
A note on how a RAID will treat drives of different sizes: If you attempt to RAID disks of different sizes together it will treat all of the disks as if they are as big as the smallest disk in the RAID. (the exception to this is a RAID option where "spanning" is involved, each disk is full size in that case).
WiebeTech offers several products which include hardware RAID controllers.
| RTX IR (iSCSI) |
High End option
Advanced RAIDs at 100MB/s at great distances (great when quiet is needed) |
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| RTX UR (Ultra320 SCSI) |
High End option
Advanced RAIDs at 320MB/s |
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| RTX200-QR |
2 disk hardware RAID
exactly what you need for RAID 0 or 1 |
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| RTX 400 RAID units |
4 disk hardware RAID
allowing advanced raid options (such as the popular RAID 5) |
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| RTX 600 RAID units |
6 disk hardware RAID
many RAID options. Available with very fast high-end connections. |
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| RTX 800 RAID units |
8 disk hardware RAID
many RAID options. Available with very fast high-end connections. |
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WiebeTech also offers JBOD products which lend themselves nicely to software RAIDs.
What's a hot spare?
A hot spare is a drive that is not used in a RAID set until a drive fails. When a drive fails, the hot spare replaces the failed drive. An enclosure that supports a Hot Spare feature can automatically sense when it's time to use the new drive, and begin the recovery process even if no human is around to trigger it.
If this should happen to you, simply replace the bad drive with a new drive, and the RAID array will be able to recover itself again if a drive goes bad.
What does "N-Way Mirror" mean?
This simply means that a drive can be mirrored to as many drives as you like, all at the same time. If any of the drives should go bad, the data still exists in its entire form on every drive in the mirror. Using this feature gives less available disk space, but provides extreme levels of saftey.
Some use this feature to duplicate disks as they go - using some disks as offsite backup, and using other disks to give to clients.
What is Offline Array Roaming?
This feature means that you can remove the disks in the RAID, mix them up, put them back in (in any order) or even put them in a different compatible unit for access.
What is S.M.A.R.T.?
Self Monitoring and Reporting Technology
The purpose of SMART is to give warning of impending drive failure before it happens, while there's still time to do something about it (such as copy the information to another drive).
Tips for buying a RAID solution
Pick hard drives that are all the same size.
Using different sized hard drives will likely result in losing some available capacity.
For example if you were to RAID 0 (stripe) two disks together and one was 250GB while the other was 400GB it would treat them both as if they were 250GB giving you 500GB of total usable space instead of 650 (the answer to why is on this page).
Don't forget about the bandwidth of your host interface.
For example FireWire can handle about 55MB per second. If you're buying an RTX and using FireWire as a host connection, there's no reason to spend the extra money on 10,000 RPM drives, as it will reach full potential of FireWire with less expensive drives and you can achieve all of the benefits of the safety of your chosen RAID level (including RAID 5).
Consider both safety and speed.
Are you archiving your important data? Pick a safe solution such as a RAID 1 mirror or a RAID 5 with a parity drive. Or, perhaps you're a video editor and you only need a volume temporarily, but you need it to be really fast - consider a RAID 0.
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