Raid on the same cable...

[cpals]

I want to setup two raid installations in my computer; one will be a Raid 0 setup for my main OS and the other will be a Raid 1 for all my backup files/misc files. Would it be better to have each raid setup on their own cable, for example the Raid 1 setup would be on one ide ribbon and the Raid 0 setup would be on it's own ide ribbon (one master/slave). Or would it be better to have it so that each raid drive is on a separate ribbon.

Example:

Hard Drive 1 (Raid 0) == Hard Drive 2 (Raid 1) == Raid Connector Slot 1

Hard Drive 3 (Raid 0) == Hard Drive 4 (Raid 1) == Raid Connecter Slot 2

 

[cpals]

*bump*

 

[chocoruacal]

Each hard drive on its own cable.

 

[cpals]

Originally posted by: chocoruacal
Each hard drive on its own cable.

That's impossible if I only have onboard raid (two inputs) and I want 4 drives for raid.

 

[Confused]

I would put them as you suggested, with the drives for each array on seperate cables. Because it would probably be seldom that you are writing to/from both arrays at once.


Confused

 

[Lord Evermore]

You will lose significant performance by having two drives on cable in a RAID array. Only one IDE device can transfer data at a single time on a cable, so you end up with the throughput of only one drive rather than the speed of a striped array. Slight latency reductions would be the only possible benefit since commands can be sent independently so the data stream can be continuous if there's enough data being requested or written.

By having RAID0 on one cable, you don't get the full performance of striping. By having RAID1 on a single cable, you don't get the enhanced read performance (normally RAID1 reads half the data from each drive simultaneously so it transfers in half the time; in this case it'll only be reading one at a time), and write performance is limited to the point that you actually get half the speed if they were on separate cables. Since the data has to be duplicated to both drives, it first has to be written to one, then the other, taking twice as long for the data to be stored.

Promise specifically markets the TX4 and TX4000 controllers for people who need 4 drives arrayed, specifically for this reason.

You can mitigate some of the performance lost I believe, depending on the usage patterns, by laying them out like this:

channel0 -- drive0 (RAID0) master -- drive1 (RAID1) slave
channel1 -- drive0 (RAID0) master -- drive1 (RAID1) slave

With this setup, during normal usage your striped array can get the best performance possible. When you store files to the mirrored array, it can be written as quickly as possible, and also read as quickly as possible. However it's still dependent on you ONLY transferring files directly to/from each array, not operating both at the same time. So if you're ripping a DVD to the mirror array (no processing), your performance in other tasks will suffer since the mirror array is receiving the DVD data and the striped array has to take away throughput from it. Also if you transferred files from one array to the other, performance will be kind of bad, but probably about the same as transferring huge files between two non-RAID drives on the same cable, or between partitions on a single drive. Overall though, this would work better than your original layout since during normal usage of only one array (all your browsing and gaming and whatever would only need data on the striped array); you would probably see reduced performance if you tried to game while you had a background app downloading several things.