purpose of raid
- Thread starter chuck990
- Start date
There are different types of RAID with different numbers of drives and different methods of writing data, either for redundancy, performance or both.
http://en.wikipedia.org/wiki/RAID#Purpose_and_basics
http://en.wikipedia.org/wiki/RAID#Purpose_and_basics
To save people readng through that (although it is certainly veryuseful and worth a read, there are two main types of RAID:
Mirroring
and
Striping
Mirroring offers redundancy. In other words you have two or more drives which mirror each other. So if you have two 500gb drives then they are written to at the same time. In the event of a failure of one drive, you still have the data on the other drive.
Striping offers faster throughput. In other words you have two or more drives and the data is spread across both. But on each drive is a different bit of the same file. So two bits of data can be read at the same time. This improves performance but is more risky because a failure of one drive means you lose everything (and with two drives you are therefore twice as prone to data loss).
There are other combinations of RAID which combine both mirroring and striping.
RAID = Redundant Array of Inexpensive Disks.
Mirroring
and
Striping
Mirroring offers redundancy. In other words you have two or more drives which mirror each other. So if you have two 500gb drives then they are written to at the same time. In the event of a failure of one drive, you still have the data on the other drive.
Striping offers faster throughput. In other words you have two or more drives and the data is spread across both. But on each drive is a different bit of the same file. So two bits of data can be read at the same time. This improves performance but is more risky because a failure of one drive means you lose everything (and with two drives you are therefore twice as prone to data loss).
There are other combinations of RAID which combine both mirroring and striping.
RAID = Redundant Array of Inexpensive Disks.
Associate
- Joined
- 26 Jan 2006
- Posts
- 2,039
Is there no speed increase from using mirroring then?
Soldato
Just don't make the mistake of being 100% reliant on the RAID5.
It's handy because you can withstand a physical disk failure, but I've been reading more and more stories of logical RAID failures too.
I've suffered a few losses recently and decided to go RAID5, and every week I catalogue (just by doing a dir > name.txt) and storing that on the web of all the files I know I can get back if required for various sources. For everything else I put it on an external drive stored here, which I then mirror with another that's stored at my parents when they come down or I go up there.
Not a massive chance of losing the RAID, but there is still a chance 1 way or another, and I'm not going through the hell I went through to get my data back like last time!
Yeah, the PSU died in my File Server this week, and when I connected the new one back my drives were showing up on my Perc 5/i as split between three different foreign configs, so i couldn't simply reimport it.
Luckily when I cleared all config data and then created a new array with same stripe size and the disks in the same order, and told it not to initialise, the volume popped back up in windows and everything was there.
Consistency check completed fine and all the disks were healthy but it's got me a little worried - still it's only media, if I need to I can always shell out for Virgin 50Mb and have it back to normal in a few weeks.
This depends on the RAID controller*, some RAID controllers will give a performance boost in RAID 1 on sequential reads by reading data from both disks simultaneously (Almost as if it were a RAID 0 array). There is no performance benefit for RAID 1 when writing though.
*The most comon RAID controller these days is the intel matix controller present in ICH7R ICH8R ICH9R and ICH10R equipped intel chipsets. These controllers do not read simultaneosly from each disk in a RAID 1 array, and so will not perform better than a single disk in when using RAID 1.