Raiding hard-drives

rmg1

Hi all

I'm looking at installing extra hard-drives for a friend and I'm after some advice.
He wants 4 (for reasons best known to himself) with the following set-up:-
2 drives striped for normal use
2 drives striped for back-up.
He's also looking to mirror the first two onto the second 2.

A few questions:-
1) Is this possible (I'm assuming it is).
2) Is this the best set-up for what he wants?
3) what's the redundancy like on a set-up like this?

GunJack

all drives in one case running off same PSU ??? I wouldn't, just in case the psu goes and takes them all out. Unlikely, maybe, but would you want to chance it ?? RAID also has it's own issues in cases of disk failure.

rmg1

I've been doing some research on RAID and it's left me a lot confused.
I'm not sure of the physical set-up as yet just wanted advice on the logical side.

messes

I wouldn't worry to much about the PSU taking out all four drives, if it's a decent PSU it should blow up first. You're more likely to encounter a disk failure first. Enterprise class servers which have redundant PSU's only use one at a time to supply to components.

What you're proposing to configure here is a RAID 10 array (check Wikipedia for more info), a combination of mirroring (1) and striping (0). This is one of the most redundant RAID arrays, but you sacrifice more disk space to achieve it.

The best way would be to do this entirely in hardware if supported. Alternatively you could create a hardware mirror using two of the disks and then use software to stripe the mirror. You may also be able to use software to do it all, but be aware that a software RAID will not move between operating systems. e.g Window to Linux.

rmg1

It will all be Windows based so no issues there.
He's looking at 4 x 1TB drives which should keep going for quite some time so space shouldn't be an issue.

messes

Keep in mind that in a RAID 10 arrangement this will only mean 2TB of usable space.

Check if the onboard SATA controller will support RAID 10, some of the newer ones may.

rmg1

Is that per set or overall?

paddyrg

He'll get ~2TB of space of course, but it may be worth discussing with him if it really is the optimal option - for instance if it's for large file i/o the striping may not increase speed, and the mirroring onto a striped set may be less robust than hoped (if they're all running in the same rack!).

There's some art as well as science, but if you post here exactly what your mate wants to achieve there may be other, better solutions. For instance, ruggedness, or large files written fast, or large files streamed/read fast, or lots of little files/data accesses (eg database access). If you post here, you may get more ideas about how you can arrange the discs more optimally

esuhl

Unless you have an expensive, dedicated RAID adapter, you will no doubt be using a "fakeRAID" firmware controller on your motherboard.

These firmware implementations of RAID are proprietary. If the RAID controller dies, there might not be any way to access the drives unless you can get hold of an identical motherboard with an identical firmware revision. I know a few people who have lost data this way.

It might be worth striping the drives that you keep the OS on (or maybe even your data if you backup regularly), but there is no way I would risk using fakeRAID for any kind of backup drives... Mirroring using fakeRAID really doesn't provide any redundancy if the RAID controller goes kaput, and do you really care how fast you can read/write backup data...?

rmg1

It's for databases access.
There's be one big upload in a morning followed by loads of little (and some big) reads during the day.
He wants some sort of redundancy (hence the backups).

paddyrg

rmg1 wrote: »

It's for databases access.
There's be one big upload in a morning followed by loads of little (and some big) reads during the day.
He wants some sort of redundancy (hence the backups).

That would suggest initially that the backups don't need to be striped necessarily, and don't need to be fast (so don't increase the risk of loss with a raid 0 stripe).

Does the upload (you say big - how big is big?) need to be fast? Do the reads need to be fast? Sounds like this is/should be a server application so you should look more at how to configure the diskset for the database engine to get the most out of - what database engine is it? For instance data files on 1 diskset, transaction logs on another will make a bigger difference than raid0

Also, fwiw, in a 4 disk setup suggested in post 1, there seems to be no place for the operating system to boot from or for the database and other server systems/software to live - unless that's a 5th disc?

Just thinking aloud, but raid 10 sounds sub-optimal to me just now.