RAID calculation formula

noir911 · 07-16-2009, 06:33 AM

I understand different RAID levels but confused about the formula to use in calculating the disk space it would take. Eg. if I have 6x200GB disk and do RAID 5, how much disk space will I have? With the same scenario, how much disk space would I have if I do RAID 1+0 or RAID 1?

I have read http://compreviews.about.com/od/stor...aRAIDPage1.htm but the calculation/ wording is not very clear on this one.

Thanks.

pi314 · 07-16-2009, 06:42 AM

With RAID 5 you loose the space of 1 disk.
eg. 6x200GB in RAID5 -> 1000 GB

With RAID 1 there is a "backup disk" for each disk so you loose half space
eg. 6x200GB in RAID1 -> 600 GB

With RAID 1+0 you make RAID 1 arrays and then you combine them using RAID 0, so basically you loose half space
eg. 6x200GB in RAID1+0 -> 600 GB

noir911 · 07-16-2009, 07:10 AM

Quote:

Originally Posted by pi314

With RAID 5 you loose the space of 1 disk.
eg. 6x200GB in RAID5 -> 1000 GB

With RAID 1 there is a "backup disk" for each disk so you loose half space
eg. 6x200GB in RAID1 -> 600 GB

With RAID 1+0 you make RAID 1 arrays and the you combine them using RAID 0, so basically you loose half space
eg. 6x200GB in RAID1 -> 600 GB

Thanks for the explanation. Your explanation is much better than what I've read.

If I have 6x300GB disk and I do RAID 5, I will loose 300GB and will be left with 1.5TB disk space, right?

What if I have 3x300GB and 1x100GB and 1x200GB - how much disk space will I loose in this case?

Thanks.

pi314 · 07-16-2009, 08:34 AM

Quote:

Originally Posted by noir911

If I have 6x300GB disk and I do RAID 5, I will loose 300GB and will be left with 1.5TB disk space, right?

Right.

Quote:

Originally Posted by noir911

What if I have 3x300GB and 1x100GB and 1x200GB - how much disk space will I loose in this case?

I'm not sure if you can build a RAID 5 array with hard disks of different size. Does anybody know?

valen_tino · 07-16-2009, 09:02 AM

Usually with hardware RAID, the drives should be identical.
However, with software RAID the drives need not be identical.

ADxD_7 · 07-21-2009, 03:59 PM

Quote:

Originally Posted by noir911

Thanks for the explanation. Your explanation is much better than what I've read.

If I have 6x300GB disk and I do RAID 5, I will loose 300GB and will be left with 1.5TB disk space, right?

What if I have 3x300GB and 1x100GB and 1x200GB - how much disk space will I loose in this case?

Thanks.

When you use disks of varying sizes in a RAID5 setup(I have only done this with zfs) you lose the space of the largest disk, i.e. - 3x300GB and 1x100GB and 1x200GB, you will lose 1x300GB disk -

But dont forget to take a spare into account

.