Topic: 5400rpm drive + 7200rpm = raid ok?

[Len]

is it possible to use a 80gb 7200rpm drive with a 80gb 5400 drive as raid?  



thanks

[chris]

hello,,,  
  if you are using a hardware RAID it cannot be done cause you have to use the same size,manufacturer,capacity hard drive


you can use it using software raid

[Dub Dublin]

Yes, it's possible, but there won't be any speed improvement if they're mirrored (RAID 1), since you'll still only be as fast as the slowest disk.  (In fact, it wouldn't surprise me if this is a bit slower just because the read/write cache managment effort goes up.)

If you're striping/concatenating (RAID 0, and the last time I checked, true striping wasn't available in Linux' RAID), it should make less difference, but things could get pretty weird where they join together.

This is based on considerable RAID experience, but none of it under SME.  The principles are constant and should hold, but implementation details could change the outcome.  (I use hardware RAID on my SME boxes - I find it's well worth the minimal extra money and is entirely OS-transparent.)

[Len]

cool thanks, just wanted a backup to my main drive via software sme raid

[David Pennycuick]

Len wrote:
>
> cool thanks, just wanted a backup to my main drive via
> software sme raid


I think the docs say that you can't convert an existing single drive system to raid.  You probably have to reinstall......

regards

David

[Kelvin]

Hi Chris,

> if you are using a hardware RAID it cannot be done cause you have to use the
> same size,manufacturer,capacity hard drive

This is absolutely not true. You will find that most hardware raid docs will recommend you use the same drives to maximize usage of the drives and performance. However, you absolutely *can* use drives from different manufacturers, etc. with hardware raid controllers. The lesser of all specs (ie. size, speed, etc.) determines the final size, performance of the RAID disk (at the time the RAID drive is being built).

Consider this. Most drives are fairly reliable. As such, most drives will perform well past their model lifetime. By the time one of the drives fail, there is a good chance that you won't be able to buy one of the exact model again, therefore requiring you to replace it with one of a different model / manufacturer which most likely will differ in specs in one way or another. If the hardware raid cards don't allow this, your RAID will not be worth the silicon their built on as you will then have to replace not one but BOTH drives. The only requirement you need to meet (and this also applies to software raid), is that the replacement drive must NOT be of a lesser capacity than the one you are replacing.

My 2 cents.

Kelvin

[Ralph]

Hi Len,

have to agree with Kelvin - no concerns about rpm and size(s) - smallest one will result in final size.

Migrating from single to raid 1 - either using hw or sw raid - will result in a total loss of data on the original drive - means reinstall and restore from backup ( usually done within max. 1 hour ).

cheers,

Ralph

[Kelvin]

Hi Ralph,

Actually, most of the hardware mirroring (RAID 1) controllers I have come across allows you to create a mirror from a drive with existing data without losing any data. How you get the driver into the existing Linux configuration however is beyond me but I'm sure it has been done before - just search the forums.

OS independent mirroring chassis systems like the Accusys 7500 - even easier - no drivers to worry about at all.

RAID 5 controllers on the other hand, you can't.

Kelvin

[Bo]

Why not mount the slower disk and reconfigure flexbackup to do backups to that disk? /Bo