RAID

[Jonathan Oakes]

I am going to buy two 40Gb 7200rpm hard-drives and I wish to connect them in RAID. I am not 100% sure though which RAID setup it is to make the two hard-drives act as one, so when a 1Mb file for example is writen to the joined hard-drive it will write 0.5Mb to each hard-drive increasing the speed of file transfer. I think it is Strip Array but I am not sure can someone please help or I will just set them up every way until I am succesful.

Thanks

[Graeme*Kustom*]

moving to hardware section...

[The Pimp]

RAID 0 aka Striping is what you are on about & requires at least 2 drives. RAID 1 is mirroring where it will put the same information on the 2nd drive as the first incase of problems & also requires at least 2 drives. RAID 0+1 need 4 drives and will stripe all four into 2 drives and use the second stripe as a backup incase of problems.

[Jonathan Oakes]

Thanks. I was gonna rate you but the wee thing majig never popped up the left hand side. Sorry about that but anyway thanks again.

P.S. does the RAID 0 of your work really well and does it make the to hard drives act like 1 14200rpm hard-drive, just a theory.

[Dead_One]

Is limited by the speed of the controller, so not as fast as a 14400 drive, but a lot faster than a single drive.
Course, if one drive fails, you loose all your data.

You might be better going for 3 drives and a striped parity drive......

[Graeme*Kustom*]

yeh but if you're using a single drive and it fails, you lose your data !! I always wonder why there is extra concern over the way that raid 0 loses everything ... I guess there is a little extra stress on the disk...

[Rim Block]

Raid being developed for scsi drives in an enterprise environment means that now it has filtered down to the home user and to ide drives that the people who seem to know the most about it have been using it in the environment where it was originally intended.

If raid is being used in an enterprise environment then obviously redundancy is usually a requirement rather then a nice extra.

Bear in mind that as stripeing the disks generally puts half the data on each disk (depending on cluster size, see below), both disks are in theory used an equal amount and would therefore be much more likely to reach their MTBF mark a lot sooner than if you used them as two independant drives.

If you are just going for storage capacity (which it would appear you are not) then Win2K and XP allow you to mount drives on folders therefore creating one large drive as you can in Unix.

Raid 0 will not double your speed but it will increase the speed noticably especially if you stripe your system partition. You need to factor in the latency of both drives (time for the head to reach the sector to be written to or read from) and the effect of the stripe size.

Loads has been written on the effects of different stripe sizes but to summerise....

If you have a 1Mb file to write to two striped disks for example;

Having a stripe size of 512k would allow the controller to split the file into two chunks and send each chunk to one disk which would then have to find one sector each and write one 512k chunk. This would be very fast.

Having a stripe size of 128k would mean the controller would have to spilt the file into 8 chunks then send 4 chuncks to each drive which would have to find and move to 4 sectors to write the chunks. This would be slow

Say you have a stripe size of 1Mb. The controller would just pass the file to one of the drives which would then write it as if it was a single drive giving you no advantage of having the drives striped.


The inverse of this is trying to write a 128k file.

Stripe of 512k = written to one disk, waste 384 (rest of the sector)
Stripe of 128k = as above but with no wastage.
Stripe of 64k = Split between two drives so speed increases with only one chunk going to each drive.

The reverse is also true for reading the file. Depending on the stripe size, the drives may have to read multiple sectors on each disk or just one sector from one disk.

I tend to keep any data I do not want to loose (saved games, docs etc) on an old unstriped drive and just backup any modified files when I need too.

Although not ide specific, there is a lot of info on Raid on the Adaptec site and in the SCSI newsgroups (try searching via Google groups).

Right thats it for now (*pant*). Gotta rest these poor fingers.

Hope it helps

Rims

[Lee Oakes]

Cheers for that, evry1. ;) .
I've gotta hold of a 5400rpm drive whicht he OS will be stored on , then im gonna have my big badass storage using the 80GB of raid space. C: drive will be 8Gb and the D: will be 80Gb.
OS will remain trusty old win98.

Evry1 happy with that? :cool:

[RAD-UK]

I can honestly say that RAID is worth it.

Just recently I have updated my 2x 80 gig IBM drives to a new additional pair.

Im running 2x in RAID 0 on an ABIT AT7
and keeping 2 for general backup of videos mp3 & stuff I dont want to loose.

The performance is very noticable.

Applications like word / Outlook express etc that perhaps took a few seconds now just bouncy on screen.

Im a happy camper for one....