How do I verify that my RAID 0 is working?
January 9, 2014 3:37 PM   Subscribe

I just purchased a G-Tech 4TB drive that was striped for RAID 0 (mac). I only see the one drive on my desktop–as I should–so how do I verify that the drive is working correctly and making backups to both paired drives? Is there a mac utility or do I just pray? Any help would be much appreciated.
posted by captainscared to Computers & Internet (17 answers total)
1) If it's RAID 0, it's half the data on one drive and half on the other. You lose one drive you lose all data. RAID 1 is what you want

2) You can test it by unplugging one drive and seeing if the system still works. If it does, you're good (RAID 1). You'll have to spend a couple of hours rebuilding the volume after.

You could also verify in the RAID bios that it's enabled. If you're seeing only one drive in the OS then it's likely working.

posted by Sonic_Molson at 3:44 PM on January 9, 2014 [1 favorite]

If it's really RAID 0 (striping), there's no redundancy at all. If one of the two drives go out, you lose all of your data. RAID 0 solely exists for speed. If you want redundancy, RAID 1 is what you want. If you really want to test it, unplug one of the drives and see if your data is still there.

On preview: what Sonic_Molson said.

One thing to keep in mind is that RAID mirroring/parity is not backup. It only protects against drive failure. It won't protect against accidental deletion, file corruption, failure of both disks, etc.
posted by zsazsa at 3:49 PM on January 9, 2014 [2 favorites]

So how do I convert RAID 0 to RAID 1 on a mac?

posted by captainscared at 3:51 PM on January 9, 2014

For starters you need to buy a second drive.
posted by phaedon at 3:55 PM on January 9, 2014

RAID != BACKUPS, repeat forever.

Also, are you saying you only have one drive? If so you should start with the wikipedia page on RAID and maybe talk to a more techish friend about this.
posted by Cosine at 3:57 PM on January 9, 2014 [3 favorites]

Assuming you have the G-RAID, it looks like only RAID 0 is supported, so you'll need different hardware.
posted by ckape at 4:18 PM on January 9, 2014

RAID != BACKUPS, repeat forever.

After working in IT for a little over a year, I strongly agree with this statement. Since you have a mac, the best backup option is to get an external drive and use the built in Time Machine utility. RAID 0 is used to make two separate drives appear to the computer to be one drive, RAID 1 is the mirrored configuration, but it is NOT a stable or good backup method. Sorry for the bad news but it looks like the other comments here are right and you need new hardware, unless you just want to use this 4TB as a backup, in which case you should just use it for Time Machine.
posted by KeSetAffinityThread at 4:25 PM on January 9, 2014 [1 favorite]

RAID 1 is great for high speed data access (assuming you've also got a high RPM drive). If you are trying to optimize a SAS machine, RAID 1 helps maximize crunching through your WORK library, so if you are doing a metric ton of sorting, joining, and looking up - you can minimize your access time once you are filling your memory and generating page faults from a query.
posted by Nanukthedog at 4:42 PM on January 9, 2014

Of course, the new way to go is SSD...
posted by Nanukthedog at 4:44 PM on January 9, 2014

REMEMBER: The rule to live by with RAID 0 is that the zero stands for the amount of data you will be able to recover when one of the drives fails.
posted by laconic skeuomorph at 4:45 PM on January 9, 2014 [4 favorites]

Is there a mac utility or do I just pray?

RAID 0 is fast — fast like riding a motorcycle on the edge of a cliff at night with the headlights off. Fast is fun, but wear a parachute — make backups to another drive — or spend all your time praying that your data are okay.
posted by Blazecock Pileon at 4:48 PM on January 9, 2014

RAID0 is twice as fast, but it's also twice as failure prone: more drives = more failures. But "twice as failure prone" is not as "certain doom" as Blazecock Pileon's hyperbole states, though. Something like 94% of drives make it to 3 years old. So there's a less than 15% chance you'll have trouble in the first three years.

So you want a different device to use for backups. But this is a great device for day-to-day use. And as people say, having a redundant RAID only protects you against hard drive failure. It doesn't protect against software failure, user error, or RAID controller failure. So no matter what your day-to-day storage, keeping separate backups is a very very good idea. If you have little enough data that configuring this device to do redundant RAID would be viable, I'd suggest just buying a 3TB external drive and using that with time machine for backups.
posted by aubilenon at 6:00 PM on January 9, 2014

Also, and you may think this overkill, I backup my data to another drive in another machine AND keep a copy of important stuff (legal stuff, photos,etc) on DVD in a safe place at work as well as in the cloud.
posted by Cosine at 6:03 PM on January 9, 2014

FWIW, I use RAID 1 as a way to protect against data loss due to hard drive failure, but I also back up the RAID 1 to another RAID 1 pair. I have a bunch of music I don't want to lose, and I stream the music from the RAID 1 server, which I simply regularly back up with SuperDuper! to another RAID 1 just in case a controller goes bad or something else happens that destroys the original RAID1. So in that sense RAID 1 can be a backup, but not just by itself, rather another RAID 1 can be a backup to the first RAID 1.
posted by VikingSword at 6:28 PM on January 9, 2014

It is possible to base a backup strategy on abuse of a RAID 1 controller. But you will be rightly mocked for doing so.

With RAID 0, you can tell if it's working by checking that you see a single filesystem whose size is the sum of the sizes of the physical drives connected to the RAID controller, and that the filesystem passes the usual consistency checks.

With RAID 1, you get a filesystem the same size as each individual drive attached to the controller. For example, a pair of 2TB drives configured for RAID 1 gives you 2TB of space, not the 4TB you'd get from the same drives configured as RAID 0. A RAID 1 array can, in theory, survive the loss of either drive; it maintains identical content on both unless one has just been replaced, in which case it will be in the process of copying everything from the remaining good drive to the replacement.

RAID 5 gets you the sum of all connected drive capacities, less one drive, and can in theory survive a failure in any one drive. So if you had three 2TB drives connected in RAID 5, you'd end up with 4TB of available space.

RAID 6 gets you the sum of all connected drive capacities, less two drives, and can in theory survive a failure in any two drives. For example, four 2TB drives configured for RAID 6 would get you 4TB of available space.

RAID 5 and 6 are both much slower than RAID 0 and RAID 1 if implemented in software, because the CPU needs to process every single byte written to the drives. With a dedicated hardware RAID controller, they can offer comparable speeds.

The reason for the "in theory" caveats above is that RAID controllers tend to declare a drive "failed" as soon as they detect a single bad block on it, and it may well happen that the act of rebuilding a degraded RAID array after replacing a failed drive will cause the controller to try to read bad blocks it would not have encountered in normal operation. This makes it declare the associated source drive "failed" as well and refuse to rebuild further from it, even though the filesystem might well have ended up perfectly usable had it done so.

This leads to one aspect of best practice when using RAID 1-6: try not to make all the drives connected to the controller the same make and model; just make them the same nominal size. Drive failure is better correlated with drive age than with any other factor, and you want to minimize the chance that the first bad block the controller sees is one of several that have appeared more or less concurrently across the whole array.
posted by flabdablet at 7:06 PM on January 9, 2014

Nobody has really answered your question here, but you do seem to have a misunderstanding of how RAID works, and I can't address your particular question because I don't know Mac. But I will say that RAID 0 is the opposite of backup. You use RAID 0 when you want performance, not resiliency. RAID 0 actually decreases data "resiliency" (as others have said, if you lose one drive, you lose everything) If you want resiliency, you need RAID 1 (mirroring) or RAID 5, 6, 10, etc...

To put it simply, if you've only got 2 drives, and you want your data protected against drive failure, your only option is RAID 1.
posted by Diag at 4:47 AM on January 10, 2014

Interestingly, Seagate just released a RAID-0 external backup drive at CES, called the Backup Plus Fast.
posted by smackfu at 5:51 AM on January 10, 2014 [1 favorite]

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