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Adding an external RAID array

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July 9, 2010 2:28:55 PM

Hey there folks,

I have a pretty good system (i7-920 with 12GB, two Velociraptors in RAID 0 for the system disks) that I'm trying to make better by adding an external RAID array. I will use it for backing up the PCs in my home network (about 6), as well as for serving media (music and video).

I was thinking about doing the following:

Buy this external enclosure: SANS DIGITAL TowerRAID TR5UT-B 5 Bay SATA to USB2.0 / eSATA Hardware RAID 5 Enclosure

Run RAID 5
Purchase 5 2TB SATA drives
Keep one drive in hot-standby providing 6TB of redundant storage.

a) What do y'all think of this plan?
b) What drives would you recommend for the system?

Thanks in advance,
Jerry
a b G Storage
July 9, 2010 3:08:18 PM

If you're using it primarily for backing up a variety of PCs, have you considered a NAS?
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July 9, 2010 3:48:18 PM

I run this computer 24/7 anyway, so what's the advantage? I can access the data on the drives a variety of ways this way, either through SMB or via programs like a uPnP server, iTunes server, DVArchive, etc. I can also use a VPN client on the computer to allow secure access to the data across the Internet; with a NAS, I'd be reliant on the box's firmware to support a protocol I would be comfortable with - a security bug might exist in the NAS firmware but firmware tends to update infrequently, whereas if a security bug is found in the VPN client I'd be able to get the update fast or to switch to a different VPN without the bug.
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a b G Storage
July 9, 2010 6:32:31 PM

Well, that was one of the questions - if the PC is on 24 x 7 that removes a problem. Another would be the issue of something happening to the PC that would affect local storage, although external storage with separate power removes one problem.

There's also an issue that has been documented, with very large raid 5 arrays, your chance of a soft error go up with the amount of data stored, so for that much data you have a reasonable chance of not being able to complete a rebuild due to soft errors. RAID 6 eliminates that issue, as do devices that periodically check integrity.
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July 12, 2010 2:33:35 AM

After looking over RAID options I'm now leaning to go to RAID 10 which will put 4 MB online instead of 6, but will still provide enough for a couple of years, while giving a much better level of redundancy as well as boosting speed.

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July 20, 2010 3:27:09 PM

I was looking at the documentation for the TR5UT-B some more, and it appears that it does not support RAID 10 with a hot spare drive. Moreover, it appears that in order to replace a hard drive the RAID system must be powered off. Does anyone know of a 5-disk external RAID 10 system in which I can have a hot spare (4 disks in the RAID 10 and the hot spare) and in which you can also do a hot swap after the array is rebuilt using the hot spare when a disk fails? Ideally for free lol.
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August 3, 2010 1:34:55 PM

I'm bumping this because no one responded...

I'm somewhat flexible but would like to run RAID10 (aka RAID 1+0) in which there is a hot spare and where you can also do a hot swap after the rebuild. This way the storage can stay online after a drive failure without loss of redundancy and it's not necessary to bring the array down to replace the broken drive.

It doesn't have to be a 5-disk version but that's the smallest size which will do what I ask (2-disk striping, mirrored, with the hot spare ... 2x2+1=5), so presumably it would be the cheapest.
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August 3, 2010 2:36:39 PM

I don't want to come across as a spammer but my company resells a product called DataTale from Onnto.

I use the 4 bay at home with my Windows 7 Media PC and it works great. Using 4x 1.5 Tb drives.

It comes in 4, 2 and 1 bay flavors. USB 2.0 Firewire 800/400 and eSATA

The 4 bay supports RAID 0 1 5 and JBOD
The 2 bay supports RAID 0 1
The 1 bay can be used with the 4 or 2 bay to have off site backup.

Here is the link for the 4 bay.. there is a video

http://www.amerdirect.com/_e/dept/07/Onnto_Products.htm

Anyway,

Hope this helps.

Ian
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Best solution

a b G Storage
August 3, 2010 6:00:26 PM

raid 10 doesn't need a hot spare to stay online after a single drive failure. In fact, you can have 2 drives fail (if they are in different mirrors) and not lose data.

RAID 10 mirrors 2 drives (A A) then mirrors 2 more (B B) then stripes the data across those 2 mirrors. So, if you lose one A drive, and one B drive, the array continues to operate. If you lose 2 B drives, that half of the stripe set is down, and you lose data.

The odds of losing 2 drives at the same time, short of something external (big power surge, fire, etc) I would think is pretty low. RAID 10 should give you high uptime and performance without a hot spare. Plus, since raid does NOT replace backup, and you have another copy of your data somewhere else (right?) then you have an extra level of protection.
Share
August 4, 2010 3:14:55 AM

The issue is that if a drive fails and then I'm not around to make the swap, then the array is at risk. Backup will only restore things to the point of the last backup, and if we're talking about an online database we could lose all the transactions since the last backup should a second failure occur before the bad drive is swapped out.

I know it's a low probability event but I'm looking to enhance my data security. It will be better than my current setup in any case (RAID0 with nightly backup).

If there isn't an external box that provides this, perhaps I can combine a PCIe RAID controller card that can with an eSATA-based drive enclosure...any ideas for a controller card that (a) provides RAID 10, (b) provides hot spare capability, and (c) allows hot swaps?

Thanks!
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a b G Storage
August 4, 2010 1:30:37 PM

if you have a database, your data files should be on one drive, and transaction log(s) on another (or a different array). So if you lose your raid 10 array, the db can be restored from a combination of backup and log files. For a home network, I wasn't getting the impression that you would be running something like a SQL server though. :) 

I do understand what you are saying about a hot spare though.
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August 11, 2010 2:50:45 AM

Best answer selected by jeroly.
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