RAID 5 questions

psd99 · 31 Oct 2008 at 19:40

Bare with me............

Say I had 3 X 73gb in a RAID 5 setup and eventually I wanted to replace all three to 3 X 146gb without losing any of the data on the original drives.

If I was to replace one of the 73gb drives with a 146gb drive and started to rebuild the RAID so at that moment it would be

RAID 5

2 x 73gb + 1 x 146gb would the 146gb drive be fully available?

Eventually if I replaced all of the drives with 146gb individually would my data be on them from the 73gb drives?

Hope that makes sense.

doc · 31 Oct 2008 at 21:34

In theory yes, practically no.

Drives in RAID arrays usually have to be the same size. If one is bigger it will get truncated to the size of the others. It tends to be only expensive RAID cards that will not truncate the drive, although you cannot still use the extra space.

I would advise you to just backup the data and start the RAID array on the new drives from scratch.

psd99 · 1 Nov 2008 at 07:44

thanks

Pandobear · 2 Nov 2008 at 10:24

There is little point in using Raid 5 for this type of implimentation, you would be much better off, speedwise using raid 0 or 10.

York · 2 Nov 2008 at 14:52

doc said:
In theory yes, practically no.

Drives in RAID arrays usually have to be the same size. If one is bigger it will get truncated to the size of the others. It tends to be only expensive RAID cards that will not truncate the drive, although you cannot still use the extra space.

I would advise you to just backup the data and start the RAID array on the new drives from scratch.

With a good raid card you will be able to use excess space on drives that are larger than needed to create additional raid arrays.

lay-z-boy · 2 Nov 2008 at 15:33

doc said:
In theory yes, practically no.

Drives in RAID arrays usually have to be the same size. If one is bigger it will get truncated to the size of the others. It tends to be only expensive RAID cards that will not truncate the drive, although you cannot still use the extra space.

I would advise you to just backup the data and start the RAID array on the new drives from scratch.

Er, practically yes.

Loads of NAS boxes that support multiple drives support online expansion. True hardware RAID cards also support online array expansion where you can add drives to an array and expand it or change each of the drives over to larger drives and eventually end up with an increase in space.

Pandobear · 2 Nov 2008 at 16:53

I am with doc on this one. After replacing all three drives with larger versions then you would be able to expand the partition to 2 x (the smallest drive) size, but not after one or two drives had been replaced, or rather you would still be restricted to 2 x 74GB. You are correct that you could on some cards make use of the unused remaining space to store data, but it would not be part of a raid 5 array until you have three drives or more, and at that point you could expand your existing partition.

Mercutio · 2 Nov 2008 at 17:35

I think that was the original posters idea.

3x74gb raid 5
swap in 147, rebuild
2x74gb, 1x147 in raid 5
swap in 147, rebuild
repeat till all 3 were 147gb

Make second partition?

But in practicality, yeah. Buy a 100GB+ drive. Move the data over. Unplug all the old drives. Plug in the 147's and make a new raid5.

psd99 · 2 Nov 2008 at 17:43

Mercutio you are correct there although no new partition.

The idea would be to replace all 74gb drives with 147gb drives but not losing any data at all by being able to rebuild the RAID each time.

The actual question wasn't for myself it was a question asked at work. I hadn't been asked this sort of thing before. I work in a place where RAID 5 is utilised a lot. We deal with RAID rebuilds quite regularly on a RAID 5 setup.

My answer was that the first 147gb drive would initially end up being formatted as 74gb drives because of the current RAID 5. I would also start fresh with 3 brand new drives and somehow look to migrate the data over from the original drives.

This RAID gets confusing sometimes for me.

Pandobear · 3 Nov 2008 at 18:35

easiest solution would be to build the new raid 5 array on the current machine and then use Acronis or similar to clone the partition, much quicker than three rebuilds and the partition is automatically resized to the largest available.

Zarf · 4 Nov 2008 at 16:20

Is it that you can't afford all three new drives at once, or that you don't have enough ports left on your raid controller?

You should be able to replace drives and rebuild the array three times, then expand at the end without losing any data. You'll need to expand the partition both in your Raid manager utility, and in windows.