RAIDS, or ‘Redundant Array of Inexpensive Disks’ is a very misunderstood technology, even by many industry experts.
For those of you who don’t know much about RAID’s here’s a quick explanation of this disk technology.
Levels of RAID
There are several types of raids. The whole idea behind a raid is to use multiple hard drives together to create either or both conditions:
- Higher reliability – You can loose a disk and not loose everything.
- Extended capacity – There was a time when we only had 30GB disks and needed 300GB worth of storage. Using a technology to add the storage of several disks and present it to the operating system as one disk has a lot of benefit. One being reduced complexity and the second being increased disk speed handling.
There are several configurations possible for RAID. For simplicity sake, I’m only going to cover the bare basics.
RAID 0
Raid 0 is created by taking 2 or more disks and chain their storage together. Let’s look at an example. Let’s say our system has 3 disks configured as a RAID 0. Let’s say we try to write a message that is 3 bytes long to the disks. The raid would write 1 byte to disk one, then the second byte to disk 2 and the 3 to disk 3. In other words, your data will be broken into chunks and the data would be written chunk by chunk to each disk. After you write to disk 3, it would automatically write on disk 1 again, and so on.
The real benefits of RAID 0 is speed and the increased storage abilitys.
Storage on RAID 0
If you purchase 3 160GB hard drives and turned them into a RAID 0 storage array, you would now have one logical drive that is 3 x 160GB or 480GB. You would now have a total of 480GB of usable storage nothing wasted and you wouldn’t have to worry about upgrades for a while.
Speed on RAID 0
My earlier explanation was quite simple, but you can tune a RAID 0 to make the ‘chunk’ of data the same size as the hard drives memory cache.
Every hard drive has a solid state cache built into it. The idea being, you can very quickly write the chunk of data to the hard drive and then the electronics on the hard drive can then spool it to the spinning media at a much slower speed. This increases the effeciency of the drive as well. It allows the drive to make a complete revolution on the disk for one read or write and spool the data to the disk.
Now here’s a nice trick. It’s especially good for amateur video editors in the crowd. If you set up a RAID 0 as your disk capture drive for spooling video and audio from your video camera, it is very fast and effecient storage. Here’s why. The time it takes to spool a chunk of data from memory to the cache on the hard drive is quite fast. Here’s the bottleneck. To spool the data from the hard drive cache to the spinning media takes forever in comparison to the step before.
We can make this process much more efficient by knowing how big the cache on the hard drive is. We set up or RAID 0 to have a data chunk size that is no larger then the hard drive cache. So we will write or read to the drive’s cache limit and then move to the second drive and do the same, and then the third and so on. This give the drive time to move the data from the disk drive cache to the disk drive’s spinning platters. Needless to say, this can dramatically increase disk speed. If you were able to double the disk access speed to reading and writing data, you would notice more then doubling the speed of the computer’s memory! I’ve tried and still use this procedure for video, because it just works.
RAID 1
RAID 1 is a slightly different technology. It uses exactly two disks of the same size. A RAID 1 will create a mirror copy of the first drive onto the second drive. So, if you insert two 40GB drives, you will end up with 40GB’s usable storage. Now, on the initial evaluation this sounds crazy in comparison to RAID 0. Here’s the difference. If you lose one drive in a RAID 0 configuration, you lose all the data on all drives. You need all the drives to recover the data. In a RAID 1 configuration, you can lose any one disk and not lose anything! I use this setup when I setup and install Linux servers in client customer sites.
RAID 1 – Speed
RAID 1, if you hadn’t guessed is not as fast as RAID 0 when writing to disk. You’ve lost the daisy chain method of writing to disks and as a matter of fact, you now have to write the same data to two disks for one write sequence.
But when reading from RAID 1, we do get a bit of a speed enhancement. If your RAID hardware is able to do this, it can read a bit of information from one disk, then read more from the second. So in a way, your RAID acts like a RAID 0 configuration.
You would only implement RAID 1 for the redundancy factor. You can lose one drive and you don’t lose anything. You do have to make sure that you replace the failed drive before the only remaining drive fails too.
RAID 5
With RAID 5, you are again setting up a set of three or more drives together, much like a RAID 0 configuration. The difference is, you will reserve one disk as a checksum disk.
Let’s say we setup three disks as a RAID 5. The RAID hardware will setup disk 1 and 2 like a RAID 0. It will stripe the information between them. Now, the raid hardware will create a unique checksum of the data that was just written to both drives and store it on the third drive. The idea being, if you lose any one drive, the data can be recreated between the drives that are striping the data or with the checksum to recreate the data that was lost in the stripe set.
RAID 5 Benefit
The two real benefits for RAID 5 are:
- Increased storage space. When you put five 100GB drives together, you will end up with 400GB of usable storage space. Remember one drive is reserved for the checksum.
- Increased reliability. You can lose any ONE drive in a raid 5 configuration and not lose any data.
RAID Summary
That’s the real fast tour of RAID for the non-techie. You now can see the benefits to using RAID with your computer, if it supports it.
- Ability to have increased reliability. With a RAID 1 or RAID 5 setup, you can completely have one disk fail and you’ve not lost any data.
- Increased speed. With RAID 0, your read and write speeds can be much faster.
- Increased disk storage space. With RAID 0 and RAID 5, you can combine the storage amounts of several drives.
- Combination of benefits. With RAID 1 and some more complex RAID configurations, you can gain all the benefits to one degree or another.
What RAID is Not!
With the ability to have increased reliability, RAID is not a substitute for proper computer backups! Your RAID will not protect you against accidental erasure or malicious attack by a virus or computer hacker. You still need backups!
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