To RAID or not to RAID? What is the benefit?

[pmruk]

What are the real benefits of using a RAID 1 array in a two bay NAS? RAID compatible disks seem a lot more expensive than standard "Desktop" disks so is the extra cost really worth it? Surely if I store my data on one disk and the backups on the other, I should be covered if one fails? (I'll probably do some sort of weekly back up to the cloud too so if something catastrophic happens, my data should be safe.)

I was thinking of buying two WD 1TB Caviar Greens for use in a Syn DS211. To get 2x RAID compatible HDDs which are compatible with the 211 is pretty much double the money of the WDs.

Thanks

 

[msl]

The advantage of redundant RAID (e.g. RAID1) is that, if one disk fails, you won't suffer any downtime or data loss. This is different from backup.

If something stored on the RAID array is accidentally deleted then it is gone. If you have a backup then you may still be able to recover the data, depending on whether or not the data made it to the backup.

If you are using backups but not using redundant RAID, a disk failure will likely mean some downtime while you recover data from the backup. You will also have lost any new or changed data on the primary storage that was written after the last backup was taken.

You don't need special "RAID compatible" disks to do RAID. Any disk will do. "RAID compatible" disks are likely to be drives designed for continuous use and with lower theoretical failure rates.

I'm sure somebody with better information will add their thoughts if I have missed anything! Hope that helps.

 

[Jesse B]

Really the only advantage of RAID1 over conventional backups is uptime. If a disk fails, you don't have any downtime while you're restoring your data. This is only really useful for mission-critical servers.

As mentioned, if you delete and array, delete files, or files become corrupted or otherwise infected, etc., then RAID will not protect you. If you have these files backed up properly, they are still recoverable.

 

[kamina]

Personally if I'd get a 2-bay nas I'd use the other disk as a separate volume and replicate (back up) the data to it rather then using RAID. I can live with some downtime at home, and will have backups on an external disk so the files will be accessible if the NAS is down.

I'm more worried about stuff like corrupted data or accidentally deleting the wrong file at home. At the office we naturally use RAID for all storage, but then we have backups taken to tape daily, and downtime costs the company money.

 

[pmruk]

Thanks for the responses. Uptime isn't a major priority for me; I can live with some downtime if one disk fails. I also like the idea of being able to recover infected and mistakenly deleted files and folders from backup. So I guess I don't need to use RAID in this case which is good because I just ordered a pair of "Desktop" edition Seagate Barracuda 1TB HDDs. Regarding Hard disk RAID compatibility, it seems that it's something to do with the amount of time allowed for error checking. This thread on the WD community forum gives a few more details.

 

[graviton]

Backup Regime Vs RAID1

Good interesting points. I am in same position as the original post but confused on choosing HDDs. Now I see I am potentially better to use second disk for backup rather than to run RAID1. However there are some related questions on merits of RAID1 vs backup:

By not running RAID 1 will I get a performance advantage ?

What backup regime would be possible and logical ?
Can the NAS run a daily incremental backup overnight or would regular incremental backups at say 2 hour intervals be feasible or some kind of backup in the background whenever idle ?

Any benefit in spreading both backup and live data over both disks ?

Any benefit in getting one fast disk for live data and one slower (or smaller capacity one) for backup within the same NAS device ?

 

[thiggins]

I do not recommend using a two-bay NAS in this way. With both drives in the same NAS there are still single points of failure in the power supply and controller.

Backup should be to a physically separate device, preferably in a different physical location.

Backup interval is determined by your useage pattern and how much data you're willing to lose in the event of a failure.

 

[graviton]

complete picture

Like many thousand of people I am adopting NAS for home use to provide shared storage, media server, mail server and centralised backup for home PCs etc. I recognise the need for backups to be held separately, but cannot afford a separate second NAS for this. I would expect to hold daily backups on the NAS 2nd drive and then copy these periodically (say weekly) to another drive attached via USB and then held in a separate location. Although I might stand to lose 1 weeks data this way, I see this as infinitely better than my current at risk position. The risk of controller/NAS failure must be very low compared with risk of say a virus infection, disk failure or accidental deletion.

Surely there should be some standardised guidance for new NAS users regarding this rather than finding myself groping around for many hours on the internet trying to sus out the best config to use on my new NAS.

Indeed this thread is now offering new users conflicting advice. I appreciate it depends on the situation, but most people will just be running a home network with photos, video, music, email and usual pile of home/homework etc files spread across different laptops/PCs/Ipods etc. Is there nowhere just a definitive "how to configure your 2 bay NAS for a home network" ?

 

[stevech]

How about two independent drives (for data) and run a program like SecondCopy. That way, if the file system gets hosed up on drive A, or drive A fails, drive B's file system would be OK. SecondCopy is a great program for mirroring selected folders/files, with a synch check done on your criteria, e.g., time intervals, when-changes occur, etc.

Rather foolproof. I do use RAID1 for hardware failure on one drive pair I use for video recording (TV) due to large file sizes, but my really important files are duped using SecondCopy to reduce the risk of a corrupt file system hosing my data.

 

[thiggins]

There may be a "definitive" How To for what you seek somewhere out there. But you won't find one on SmallNetBuilder.

What is appropriate for one person, is not for another. In the end, you need to educate yourself (as you are doing) and form your own opinion based on your needs and resources available.

In the end, it's all risk management and different folks have different risk tolerance.