Questions about RAID.

[Dennisch]

What does it do? I tried reading about it online but the level of geektalk goes a bit over my head.


I have a spare 320gb hdd lying around, and I was wondering, if I could use the spare one together with the 320 I already have inside my pc. Would it be useful, would I notice anything, speed increase with handling big files and such?

 

[tuga703]

With Raid 0 you would theoretically get double the speed but in reality the speed increase is not that massive, maybe 30-50%. You would get double the hard drive space.
HOWEVER, the chance of losing ALL your data is doubled so I would not advise using Raid 0 for holding any precious files.

Using Raid 1 it would be the same speed and size as you currently have but if one drive fails you have a backup in the other.

 

[David]

Depends on what you want to do and what type of RAID configuration you want to use. The two most common types for regular users are RAID 0 and RAID 1.

RAID 0 doesn't have any redundancy but it splits pieces of data between both drives so that reading and writing can be done in parallel. It gives you a bit of a performance increase but a failure of either drive kills the whole thing.

RAID 1 just has mirroring (redundancy) so everything is written to both disks. It may slightly increase read speeds since it should access the data from whichever disk can get to it faster but the write speed will always be hampered by whichever disk does it slower. If there is a drive failure the array can keep working as long as one drive is okay.

 

[Dennisch]

Well, the files aren't important, they are just large. And I always have an online backup.

I know what I will be doing this weekend.

 

[cjmpe]

RAID can accomplish 2 different things that may or may not be compatible:
1. a RAID 0 configuration uses 2 disks and essentially splits the data across the 2 drives which should in theory improve the access times for large files. In practice I'm skeptical that you would see much difference in a personal computer environment. This big risk with this is that a failure on 1 drive can make the data on both drives unavailable.
2. RAID 1 can also be set up with 2 disks. In this configuration, the disks are copies of each other - it is used to ensure higher availability of data. If 1 disk fails, you simply replace it and rebuild and you get your data redundancy back. Generally the worst case is you lose just a file or 2 if the failure happens during a write operation (low risk there). You can get higher read and write performance if you put the disks on separate controllers, but again in a personal environment I'm not convinced you will see a massive difference.

For either of these scenarios, you need an additional device called a RAID controller. Sometimes higher end PC's come with them, but usually not. In Canada, I can get a controller card for around $70 - approx EUR50.

You didn't say whether the existing 320GB drive in the computer is your system boot disk - I assume it is. If that is the case, you will need to expect to do a complete OS re-install because the RAID conversion will wipe the disks.

 

[Dennisch]

No, it is not the system disk. It's my let's dump this file onto this disk disk.




Btw. just found out my motherboard doesn't support RAID, and as I have no PCI slot left for a controller, this has to wait.

 

[wfooshee]

And yeah, that part about the disk being wiped to convert to RAID is an important consideration, too.

Set up RAID on new volumes if you want to use it.

Also, I've found that if you're not paying attention, RAID 1 is no safer than single-drive volumes. In my experience, no one seems to notice that one of their drives has failed, until the second one fails and they wonder where their stuff went. It seems sometimes that the only way you know the RAID is good or not is the POST message when the controller starts during boot-up, which you'll never see if you run your PC 24/7.