External NAS RAID recommendations sought

I'm considering going for external NAS storage with RAID. I'm more concerned about reliability then performance so I'd guess RAID 1 (mirror) is appropriate.

Any comments or recommendations, or points to possibly be aware of?

Presumably it can just be connected to 4-port hub on my Netgear DG834GT?

Thanks in advance.

I have a Thecus unit, the N4100Pro. Takes 4 drives (mine currently has 4 2TB Seagate 5900Rpm drives inside) in a RAID 5 config. Performance is excellent (we can stream 2 HD movies to different streamers in the house with ease).. I've had it for more than a year now, and absolutely no issues (touch wood).

Yes, it can just be connected to a hub or a switch.

Take a look at the Synology and QNAP products. I have a QNAP 239 in a small business environment - it's been "up" for six months without issue.

I would recommend you put whatever you decide to go with on a UPS device to avoid issues - the QNAP will shut down cleanly after a user specified delay in the event of a prolonged power failure.

Thanks for these.

I should have said that it's for my backup drive, also that as my PC is not on all the time, neither will the NAS drive so UPS is probably over the top.

Just be careful - personally I wouldn't want to run a RAID array (regardless of the hardware involved) without a battery backup, especially if it was holding my backup data. Maybe that's being over careful, but I've experienced first hand what a power failure can do to a RAID array and it wasn't pretty.

In general these NAS systems are designed to be left on 24/7 (mine is in a cupboard hidden away!) - if you turn them off, make sure you go through the proper shutdown routine in the web interface.

EDIT: Just a thought - QNAP do a 1 drive NAS enclosure, which you could then backup to any old external USB drive (plugged into the NAS)... that way you avoid the raid/ups but still have a backup of your backup (this is what I do with the 2 drive QNAP 239 anyway)...

Edited by jhurrell (Wed 06-Jul-11 22:23:10)

Have you thought about Freenas??? I recently went for this and am running freenas on it.

http://www.ebuyer.com/product/253305

I am completely new to using freenas however, I read up on it on the net and its working all well so far. I would read the reviews of the machine on ebuyer then make your choice from there and the reviews about freenas,

I must admit I hadn't appreciated that RAID is more susceptible to power loss data corruption than a single drive. Thanks for that.

I use Genie Timeline to secure my data to an external drive. Then every day or so I use SyncToy to update a second copy of the TimeLine data to a second external drive, and once a week or so also use LapLink to update an independent copy of my PC's data to a third external drive, as well as using high capacity USB sticks, I've more or less come to the conclusion that using RAID is unnecessary. Perhaps my strategy is already more than adequate .

Thanks for all the comments.

I think that depends upon what sort of RAID you use. Mirroring (RAID 1) should make the system more robust, even in the case of a data loss. The chance of both disks being corrupted is less than the chance of a single disk suffering that fate.

RAID 0 is another matter and does make the array more susceptible to damage. With the current price of hard disks I see no reason to use RAID 0 in a backup role. The only possible use would be for performance considerations where security of the data was not important (i.e. a small OS partition that doesn't change and can be easily restored). Even there there are better techniques nowadays to provide performance.

The ideal compromise (IMO) is RAID 5, but that implies that you have at least 3 disks. Of course, no RAID system provides protection against other forms of corruption (viruses, deleted files, etc.) but Genie Timeline is doing that for you to a large extent.

Your strategy looks complex. Lot of manual work there.

I'm afraid I'm also a fan of FreeNAS. Ideal if you have an old PC lying about.

You could, if you wanted, build two and use the inbuilt rsync facility to clone changes from one system to the other (keep one in the house, one in the garage?)

You could also transfer data offsite using the same mechanism.

As for UPS, you can get APC brand ones off eBay for sub-£50 easily, more than enough to run a single box and a switch or two.

In the OP I said I wanted to go RAID 1, I don't like RAID 0 as the loss of 1 drive loses the data.

Yes. I can't see any way that RAID 1 can be less reliable than a single disk.

In reply to a post by AEP:

Yes. I can't see any way that RAID 1 can be less reliable than a single disk.

Well, if the probability of the controller card failing is higher than the probability of the disk failing, in a 2 disk setup, then in that situation having just a single disk is more reliable, give or take a few factors of course.

Edited by Pipexer (Tue 12-Jul-11 18:45:00)

I don't have figures to hand but, personally, I have never experienced failure of any disk controller card, RAID or otherwise. I have experienced several drive failures. It figures, as a combination of electronics and mechanical parts would be expected to be more prone to failure than pure electronics.

In reply to a post by AEP:

I don't have figures to hand but, personally, I have never experienced failure of any disk controller card, RAID or otherwise. I have experienced several drive failures. It figures, as a combination of electronics and mechanical parts would be expected to be more prone to failure than pure electronics.

I guess it's usually the dicky motherboard versions which can fail (i.e on their own or if other parts of the mobo go pop too), but, I am certain that some controller cards (onboard or not) were and are produced which are more prone to trouble than disks.

Enable your PM briefly and I'll send you an interesting link

Edited by Pipexer (Tue 12-Jul-11 18:53:15)

Enabled.

In an external RAID 1 disc setup, does the controller ensure the data is fully committed to one drive before committing to the other, or does it do them in parallel?

It would seem to me that the former is safer than the latter.

As with others I've never had a drive or controller fail, but there's always a first time...

I believe that most, if not all, controllers write the data in parallel. Sequential writes would impact performance, and I'm not sure that they would be any safer. RAID is really there to protect against hardware failure rather than power loss or filesystem corruption.

Bear in mind that almost all modern file systems are journalled, so writes are essentially atomic. Although not recommended, a power failure rarely seems to corrupt file systems nowadays. Of course, in a critical system you would use a UPS but I wouldn't bother with a backup drive. If it fails halfway through a backup it doesn't really matter; it'll fix itself next time.