Raid 1 question

First, if anyone has a good link that goes into Raid 1 configuration details it would be appreciated. I'm not completely stupid, but I am having trouble understanding something. I have a DLink321 NAS with 2 1TB drives set up in a Raid 1 config. It is used only for backups. So far I haven't been, but I know I need to store one of the drives offsite.

Question - I remove 1 drive and take offsite. I save some files to the remaining drive. What happens when I bring the offsite drive back and plug it in? Does it know that it should add the files to the offsite drive or does it mirror the offsite and delete the updated files?

What happens if I do decide to delete some files from the remaining drive and then I bring the offsite drive back?

I'm also considering a 3rd 1TB to throw into the mix so I always have 2 in the NAS. How does that affect the switching?

Thanks. Yes, I feel stupid as I'm sure I've missed this somewhere.

No you don't take disks out of a RAID set, that makes the set pointless. You have an additional hard drive that you back up onto if you have an offsite backup.

RAID1 may give a performance gain if you have a smart controller, but only if both disks are present and working.

If you want to use one drive with an offsite backup that's fine, but RAID isn't involved, just mirroring.

If one drive goes offline for any reason, the array will continue to function on the remaining drive. When you re-connect the missing drive, or install a new one, the RAID controller will rebuild the array. That means copying everything from the existing drive to the new one. I don't believe it will care that lots of files are already on the drive you reconnected. It'll simply make the new or reconnected drive look just like the existing one.

RAID1 requires an even number of drives. That 3rd drive could be used as a hot spare if the NAS supports it. That means that if one drive goes off-line, data will be copied from the remaining drive to that 3rd drive, restoring the RAID1 array.

You can do RAID5 with three drives. If one drive goes off-line, the array will live on the two remaining drives. Connecting a new drive or reconnecting the one you pulled will trigger a rebuild just like before.

RAID was never meant to facilitate off-site storage. Leave the array intact. Back it up to another NAS or USB drive which you can then take off site. You may also want to look into an off-site solution like Crashplan.

Thanks Tim & Mike for clearing things up a bit. I wasn't sure what happened when a drive was returned to the DLink NAS. Basically the only time the DLink is turned on is when I'm doing my monthly backups to it. So, let's say once I've done a backup and power the unit down I remove one of the drives and store it offsite. Then, when I'm ready for the next backup I retrieve the drive, replace it in the unit, power up, and do my backup. Would that be a decent plan?

At the moment my flow is I use the Adobe Photo Downloader to upload my images to the C drive and also have it put a copy on another internal (E) drive. I'll then use Microsoft SyncToy to copy over to an external drive. So at this point I have the images on 3 separate drives. Monthly (usually) I'll power up the NAS and copy all the new stuff including edits to the mirrored drives. I'll burn a dvd as well, although I'm not as current with doing that. I'll then go back to the C & E drives and clean them up which still leaves the images on 3 separate drives. Of course, all this is for naught if nothing is stored offsite. Given all this would removing one of the NAS drives and storing it somewhere else be the best thing to do. Of course, I would have to bring it back to do the "monthly" backup.

I'm open to suggestions to a better way.

I would forget the E drive. Leave the NAS on and back up to it instead. Pay $50/yr to backup your C drive to Crashplan for your off-site.

That would work, but it seems like a real waste of a NAS. You're basically keeping two backups, all RAID is doing is reducing the time it takes to make the backup, which seems irrelevant if it's monthly.

Rather than adding wear and tear on the device, with connectors that aren't made to be plugged and unplugged sometimes, just get two external disks.

mike_d wrote in post #14646187
I would forget the E drive. Leave the NAS on and back up to it instead. Pay $50/yr to backup your C drive to Crashplan for your off-site.

This isn't practical for the volume of data any serious photographer generates, especially a professional.

tim wrote in post #14646234
Rather than adding wear and tear on the device, with connectors that aren't made to be plugged and unplugged sometimes, just get two external disks.

Good point. I guess I could just store the unit with drives intact off site.

Some good advice from both of you. Thanks.

Is the NAS really small enough to bother moving? Honestly I see little point in having it. If you want to be sure your on site data is safe, great, use it. Just don't consider it when you think about offsite backups, get a drive in an enclosure and use that.

tim wrote in post #14646234
This isn't practical for the volume of data any serious photographer generates, especially a professional.

You have no idea how much data he has and how fast his Internet connection is.

tim wrote in post #14646381
Is the NAS really small enough to bother moving? Honestly I see little point in having it. If you want to be sure your on site data is safe, great, use it. Just don't consider it when you think about offsite backups, get a drive in an enclosure and use that.

It's not much bigger than the 2 drives it holds (7.7" x 5.1" x 4.1"). I suppose I could store the existing external instead though.

mike_d wrote in post #14646426
You have no idea how much data he has and how fast his Internet connection is.

My upload is a crappy 256k at best.

Get some 10Gbit ethernet going and run FCoE to a storage array.

Okay that's overkill.

A RAID set also is NOT A BACKUP. It is only a protection against a single disk failure wiping out all of your data. It is redundancy, NOT backup.

Anyway now that that is out of the way, an offsite disk is fine for backups. But it depends on how much content you generate if having just two rotating disks will work for you - basically, you bring one back from offsite, update it with the new content and any changes you've made, then move it back offsite. If you are adding photos weekly then that gets to be a pain. I'd go with a RAID set and then rotate an offsite disk to capture the updates monthly or so. If your house burns to the ground your RAID set is rather useless.

While what you suggest does work from a technology standpoint (as soon as you plug the offsite disk back in it will rebuild by copying all the data) its tremendously risky as hard drives are at their most susceptible to failure during that kind of operation. If the most current drive failed youd lose ALL data on both drives.

Hardware RAID systems are not file system aware, they have no concept of how much data is on the drives, whats new or old, etc. So each time you plug it in it will recopy the entire drive worth, regardless of unused space on the drives etc. This is also why they are not a backup. RAID cant protect against file deletes, corrupt files, etc. One or two can but those are far beyond small NAS units.

this is what will happen:

case 1: You take one drive out from raid you do some changes to the drive you took out and then you put it back. However, your raid remains powered off.

Nothing will happen. Your raid has no idea that one disk was changed. Dont expect the raid to synchronize your data!


case 2: same as above but raid was used with single drive.

Once you insert the second drive back and power on raid you will be informed that the new drive will be formatted, an so it will. All data from drive 0 (the one that remained in raid) will be copied to the second drive. All data on drive 1 will go Kansas bye bye

Thanks for clearing some things up. My original intent when I purchased the DLink unit was it would provide a fairly simple way to create a backup on two separate drives.