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I have 2 Seagate Barracuda Green 2TB HDD in RAID 1 using Intel Rapid Storage Technology. I use them as a storage volume, that is not accessed very frequently, and most importantly, that is not written to very often. This made me think that a continuous RAID-1 might not be the best solution to ensuring the safety of my data as it is at risk of accidental overwrite, viruses, and corrupted data.

I think a backup solution would suite my situation better (backing up the first HDD onto the second). As I was looking for ways to achieve this, I noticed you can change the update mode of the RAID-1 to be "On Request". This could effectively be used as backup, or I think it could.

Am I right to think that the "on request" mode basically turns the raid into a backup solution?

If so, does anyone know the advantages/disadvantages of using RAID-1 in "on request" mode as a backup solution over a software backup program with 2 non-raid HDD?

Finally, is there a way to automatically schedule the "on request"?

Thank You.

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As I was looking for ways to achieve this, I noticed you can change the update mode of the RAID-1 to be "On Request". This could effectively be used as backup, or I think it could.

In some way, yes. But it would be the exact same as leaving it to synchronize both drives automatically. Like some continuous data backup. However RAID solutions are about fault tolerance, not data backup. So you should never look at your RAID in the context of a backup. It's not a "backup of sorts", not even "almost a backup". It's not a backup. :)

For a discussion on this matter visit this question on ServerFault. But for a quick rundown, remember this: Does RAID allow you to recover data you just corrupted or accidentally deleted? Does a backup?

I have 2 Seagate Barracuda Green 2TB HDD in RAID 1 using Intel Rapid Storage Technology. I use them as a storage volume, that is not accessed very frequently, and most importantly, that is not written to very often. This made me think that a continuous RAID-1 might not be the best solution to ensuring the safety of my data as it is at risk of accidental overwrite, viruses, and corrupted data.

Most definitely. And hence why I left this to last (the above would help put things in context).

What I would suggest perhaps is for you to drop the RST altogether from those two drives and use one to backup the other until you get an external hard drive. Once you do, you can put them in RST mode again and use the external drive as the drive to hold your backups.

Why an external hard drive? Ideally the target drive for your backups shouldn't be connected to the same PSU (or even wall socket) your hard drives are. Any power issues could burn both production and backup drives (and the PSU in your computer can do that). But an "external hard drive" can also be a remote location on the network, like the Cloud or some online backup service.

In any case, your priority at this point is not Fault Tolerance. As you are realizing, Fault Tolerance does not make sense until you resolve Data Backup. For this reason — and because you have an available drive doing fault tolerance — removing RST and do data backup instead, seems the sensible thing to do.

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  • I understand how the best situation would be to have raid for fault tolerance, and have the raid backed up on an external drive. What I'm not sure I understand is why raid in a "per request" mode is not a backup. The old adage "raid is not a backup" used to make sense to me, until I found this "on request" mode. Now wouldn't that just be like having the raid driver copy the files, instead of having a backup software do it?
    – Didier A.
    Commented Jul 20, 2011 at 6:26
  • @didibus I won't deny you a point. But the procedures for recovering of this type of "backup" are just too cumbersome compared to more traditional methods. Here you are asked to remove disks, move them around and so forth. Neither you have a straightforward means to recover just portions of data (just these files, just those directories) after some incident corrupts or accidentally deletes your files. Essentially RAID-1 offers no backup recovery features. Simply hardware fault recovery.
    – A Dwarf
    Commented Jul 20, 2011 at 9:29
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And a Raid 1 will now allow you to back up data in rolling increments. For example, if you're working on a document and you accidentally deleted some important content, that data would be lost. If you configure rolling backups then you would be able to get your data back from a previous backup.

I've purchased and used a program called SyncBack a few years back from www.2brightsparks.com and it still proves to be useful today. I have one working document hard drive that backs up to another local disk. I have it set up with a rolling 7 day backup so I can access my previous data whenever needed.

What kind of information are you looking to back up? Are these movies, songs, documents or pictures?

Another thing I do, I have a Windows Home Server 2003 that is used to backup my computers. it keeps a rolling 6 month backup. For three computers with moderate use I'm about 90GB of backup data.

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  • That is a good point, that raid 1 can not allow for revisions of the backed up data. I also guess using raid 1 for backing up takes a lot more space, since it copies the entire drive every time. While a normal backup would only copy the files that need to be backed up, and it can allow for fancy features like encryption and compression.
    – Didier A.
    Commented Jul 20, 2011 at 6:18
  • My setup is that my OS is installed on a small SSD. My user files are backed up on my raid 1 array of hard drives. Since my SSD is a mere fraction of the size of my array, I also use the array to store large files, like Movies, Music, archived documents, pictures. What I want is that this hard-drive be also backed up onto my second identical HDD. I would also like this to be seamless, so that if one drives fails, I can just put the other in its place until I replace the broken one. That is why I thought a raid would work, not sure what are the disadvantages if I run it in "on request" mode.
    – Didier A.
    Commented Jul 20, 2011 at 6:23

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