External RAID

hypochondriac · 29 Jun 2008 at 12:51

I'm not too learned on computers, I know enough to get me by, but I wish I knew more.
My question is, is it possible to get multiple HDDs, put them into some sort of external box and set up into a RAID array? If so how would one go about doing that?

Also in a RAID1 array, it is my understanding that, if one of the drives (or some of the data) malfunctions a little the second drive makes up for it and there is no data loss. But, does the RAID software repair the data using the second drive or do you just pray the same data isn't lost or corrupted on the second drive.

Finally, a side query, is a RAID 3 setup (with a parity section on the redundant drive) inferior in data protection to a RAID 1 setup?

rpstewart · 29 Jun 2008 at 12:59

hypochondriac said:
My question is, is it possible to get multiple HDDs, put them into some sort of external box and set up into a RAID array? If so how would one go about doing that?

Yes, it can be done in numerous ways. Either with a RAID controller of some form in the external device (WD & Lacie used to do this to provide 1Tb externals based on 500Gb disks) or with multiple connections to an internal RAID controller.

hypochondriac said:
Also in a RAID1 array, it is my understanding that, if one of the drives (or some of the data) malfunctions a little the second drive makes up for it and there is no data loss.

That's the theory, the same data should be on both disks so if one fails the other is still available.

hypochondriac said:
But, does the RAID software repair the data using the second drive or do you just pray the same data isn't lost or corrupted on the second drive.

RAID1 is purely for hardware redundancy. If the data is corrupt on one it will be corrupt on the other. RAID1 is no substitute for a backup.

hypochondriac said:
Finally, a side query, is a RAID 3 setup (with a parity section on the redundant drive) inferior in data protection to a RAID 1 setup?

[/QUOTE]
Both provide the same degree of hardware redundancy in that they both can survive a single physical disk failure and continue operating without downtime. Neither, on their own, provides proper data protection, you still need a backup.

hypochondriac · 29 Jun 2008 at 17:50

rpstewart said:
Either with a RAID controller of some form in the external device (WD & Lacie used to do this to provide 1Tb externals based on 500Gb disks)

What would I need to make such an external device? a housing, the HDDs, the RAID controller, a PSU, anything else?

rpstewart said:
RAID1 is purely for hardware redundancy. If the data is corrupt on one it will be corrupt on the other. RAID1 is no substitute for a backup.

Corrupted wasn't the word I wanted to use. Say the data on one disk goes wrong, or decays, (I'm not too sure what happens what data goes wrong), the other disk will have the correct data, but will it notice the error and correct it, putting it back to normal? or will I have to cross my fingers and hope the mirror data doesn't suffer the same fate.

rpstewart · 29 Jun 2008 at 18:00

hypochondriac said:
What would I need to make such an external device? a housing, the HDDs, the RAID controller, a PSU, anything else?

You basically buy the unit complete and add your own disks.

hypochondriac said:
Corrupted wasn't the word I wanted to use. Say the data on one disk goes wrong, or decays, (I'm not too sure what happens what data goes wrong), the other disk will have the correct data, but will it notice the error and correct it, putting it back to normal? or will I have to cross my fingers and hope the mirror data doesn't suffer the same fate.

If a block becomes unreadable on one disk but not the other then the controller will likely mark the disk as bad and revert to single disk operation.

hypochondriac · 29 Jun 2008 at 18:08

rpstewart said:
You basically buy the unit complete and add your own disks.

Do you recommend any?

rpstewart said:
If a block becomes unreadable on one disk but not the other then the controller will likely mark the disk as bad and revert to single disk operation.

[/quote]

So it's like a safety net, not a regenerative array.

rpstewart · 29 Jun 2008 at 19:35

hypochondriac said:
Do you recommend any?

Haven't look at any of them in detail, I keep all my disks internally.

hypochondriac said:
So it's like a safety net, not a regenerative array.

Yeah, the nearest you'll get to self healing is a hot spare drive but that will only be used if any of the arrays on the controller it's attached to go critical.

hypochondriac · 29 Jun 2008 at 20:01

rpstewart said:
Haven't look at any of them in detail, I keep all my disks internally.

It's just most of the multiply drive caddys on the OCUK site are for slotting into cases, (bar the Drobo box things).

One last question, is it possible to split a HDD into 2 equal partitions then set up a RAID 1 array with them? or does the redundant disk in a normal RAID 1 setup normally fully break all together, rather than part of it. Therefore making RAID between partitions futile.

rpstewart · 29 Jun 2008 at 20:18

hypochondriac said:
One last question, is it possible to split a HDD into 2 equal partitions then set up a RAID 1 array with them?

Not with a proper RAID controller. Windows might (can't remember for sure) let you mirror partitions on the same disk in partition but the performance will be shocking since you would only have one set of heads doing 2 sets of writes and verifies before completing the operation.

lopkinfop · 29 Jun 2008 at 23:57

i use two 4 bay external boxes that raid the drives in raid0. i get them from a UK website that specialises in them, you could do a google search