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Buying RAID hard drives

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July 21, 2009 1:12:57 AM

I heard it's safer to buy hard drives from different places for a RAID configuration to lower the probability of them both failing at the same time. Is that reasonable or is it being too paranoid?
a b G Storage
July 21, 2009 2:33:43 AM

Being too paranoid I guess. Where'd you hear this? Getting disks from different vendors means more complicated support. You might even get your disks and vendors confused, bringing the wrong disk to the wrong supplier.
a b G Storage
July 21, 2009 7:36:09 AM

Never heard of buying from different places, but in the business IT industry I have heard of buying at different months to get batches of varying week made.

Buying from different suppliers at the same time and it's still possible to get the same batch.
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a c 171 G Storage
July 21, 2009 6:04:12 PM

quarup said:
I heard it's safer to buy hard drives from different places for a RAID configuration to lower the probability of them both failing at the same time. Is that reasonable or is it being too paranoid?

I think paranoid. The advertised mean time to failure of current hard drives is advertised at something like 1,000,000 hours. That is something like 100 years. It is small odds of two concurrent failures.

Are you talking raid-0 or raid-1 or...?
What do you want to accomplish with raid?
a b G Storage
July 21, 2009 10:08:41 PM

Quote:
The advertised mean time to failure of current hard drives is advertised at something like 1,000,000 hours.

MTTF, MTBF... etc. only assumes the drives function perfectly as intended, which isn't always the case in real life situation. Hence the practise of buying different batches of the model when used in a RAID array.

It's to avoid the eggs in one basket principle.
a c 415 G Storage
July 21, 2009 10:55:08 PM

quarup said:
I heard it's safer to buy hard drives from different places for a RAID configuration to lower the probability of them both failing at the same time. Is that reasonable or is it being too paranoid?

It's a sound principle, although in practice you're probably only lowering your chances of a simultaneous failure from something like 1 in 10,000 to 1 in 11,000 (those numbers come directly from my gut and nowhere else).
a b G Storage
July 22, 2009 9:10:51 AM

iv heard of this before - different brand/models to vary the lifespan/probability/reliability of a raid array etc

on the other hand the difference in performance/latencies may cause more harm then good...
July 22, 2009 5:09:16 PM

thanks, everybody for your help!

I had heard the concept in my OS class in college back in 2003, so I wasn't sure if it was used in practice. I'm thinking of setting up a Raid 1 NAS. As you guys said, the chances of the two HDs failing at the same time due to manufacturer defect in the same batch are very slim, so it may be mostly paranoia. FWIW, I ended up buying the same model (WD Green 1.5TB--hope to install TLER) from two vendors and hope they come from different batches.

I talked to a friend who said that HDs failing at the same time are probably usually due to other factors such as overheating (perhaps due to the fan breaking), in which case getting HDs from different batches wouldn't make a difference. He also warned he may have been talking out of his ass ;-).

Thanks for your help! :bounce: 
a c 171 G Storage
July 22, 2009 5:38:21 PM

Do you have external backup?

The value of raid-1 for protecting data is that you can recover from a hard drive failure quickly.
It is for servers that can't afford any down time.
Recovery from a hard drive failure is just moments.
Fortunately hard drives do not fail often.
Mean time to failure is claimed to be on the order of 1,000,000 hours.(100 years)
Raid-1 does not protect you from other types of losses such as viruses,
software errors,raid controller failure, operator error, or fire...etc.
For that, you need EXTERNAL backup.
If you have external backup, and can afford some recovery time, then you don't need raid-1.

I understand also that heat is the major contributor to premature hard drive failure, after the infant mortality phase has passed.
Perhaps it might be wiser to put one of your drives in an external enclosure to be used for backup.
July 22, 2009 5:54:42 PM

I was hoping to use this raid-1 on a Network Attached Storage and not worry about extra redundancies. My girlfriend and I would like to share the file storage, and this seemed like a convenient way of doing it. In the past (within the last ten years), I've had 2-year old hard drives fail, which is why I found raid-1 appealing. Do you recommend ditching raid-1 in the NAS and having a different form of backup?

Both of us have a lot of pictures and videos so we'd rather not store them on our laptops and leave them on the NAS.
a c 171 G Storage
July 22, 2009 6:40:21 PM

quarup said:
I was hoping to use this raid-1 on a Network Attached Storage and not worry about extra redundancies. My girlfriend and I would like to share the file storage, and this seemed like a convenient way of doing it. In the past (within the last ten years), I've had 2-year old hard drives fail, which is why I found raid-1 appealing. Do you recommend ditching raid-1 in the NAS and having a different form of backup?

Both of us have a lot of pictures and videos so we'd rather not store them on our laptops and leave them on the NAS.


If you store things in one place, they are vulnerable to one failure.
A NAS is good, particularly for sharing.
If you get a virus or malware on one pc, who knows what it can do to the nas?
Operator error can destroy files.
A fire where the nas is located can lose everything.
... you get the idea.

I would put a large drive in an external usb/firewire/esata enclosure and back the nas to it on some sort of schedule. Store the external somewhare safe between backups.
The backup data will be compressed, so the backup drive does not need to be the same size as the original.

If you do this, you really don't need to pay the insurance price of a duplicate drive to guard against a hardware failure. On the other hand raid-1 would not hurt, it would just cost twice as much.
a b G Storage
July 22, 2009 6:53:41 PM

Another +1 for no SPOF (Single Point of Failure). I always backup everything. In fact, imaging software (Acronis True Image or Symantec Ghost) and a portable hard drive are cheap, simple solutions.

I understand having a mirrored NAS as a decent option, but it's scary to put all of your valuable data in one place without backup.

Another +1 for worrying about operator error - single greatest security threat is the user (something like 90% or more of total security risks - most unintentional).

July 22, 2009 7:18:21 PM

Thanks for the useful advice! Frankly I'm weighing the added security of an external storage versus the inconvenience of:
1. buying an external storage at least as large as the NAS
2. having the discipline of routinely backing up the data

To address #2, maybe I could:
* back up my data from NAS to the external storage infrequently (say, twice a year)
* keep a temporary copy on my laptop(s) of data that hasn't been backed up to the external storage

That way the newest data is always backed up on my laptop + NAS, and the older data is backed up on NAS + external storage. That would save me the hassle of routinely backing up my data to the external storage without creating a single point of failure.

What do you guys think?

Also, is it worth exploring raid-0 for the NAS? I'm guessing it's not worth it since the network is too slow to make a difference anyway.
July 22, 2009 7:22:27 PM

PS: I will be mostly using 802.11g wireless, which is why I said the network would be the bottleneck, which why I'm guessing raid-0 would not make a perceptible difference in speed.
a c 171 G Storage
July 22, 2009 8:00:32 PM

quarup said:
Thanks for the useful advice! Frankly I'm weighing the added security of an external storage versus the inconvenience of:
1. buying an external storage at least as large as the NAS
2. having the discipline of routinely backing up the data

To address #2, maybe I could:
* back up my data from NAS to the external storage infrequently (say, twice a year)
* keep a temporary copy on my laptop(s) of data that hasn't been backed up to the external storage

That way the newest data is always backed up on my laptop + NAS, and the older data is backed up on NAS + external storage. That would save me the hassle of routinely backing up my data to the external storage without creating a single point of failure.

What do you guys think?

Also, is it worth exploring raid-0 for the NAS? I'm guessing it's not worth it since the network is too slow to make a difference anyway.

Now you are thinkng. Right on.
The external storage does not necessarily need to be as large as the NAS since the backup data will be compressed.
Back up data to it from time to time. I would think once a month would be about right. Most backup programs will have a scheduling/reminder capability.
You might also want to keep a clone image of your OS drive there.
July 23, 2009 5:54:55 PM

perfect! thanks for your help =)
a c 415 G Storage
July 23, 2009 8:55:06 PM

quarup said:
1. buying an external storage at least as large as the NAS
...maybe I could:
* back up my data from NAS to the external storage infrequently (say, twice a year)
It pays to be sensible about backups. If you have files which will never or rarely change (a library of photos, or music / video selections, for example) then it doesn't make sense to back them up as frequently as active files that you use and modify day to day.

I use a three-tiered system by putting different classes of files in different groups of folders and selecting those groups for backups:

* active files (e-mail, program code I write, teaching material I update and use, etc) get daily incremental and cycled weekly/monthly backups. For me this turns out to be about ~30GB of files.

* static files (music, photos, etc.) get daily incremental and monthly backups. The daily incrementals catch any new items added to the library without the bulk of backing the whole shebang up every week. The monthly backups reset the archive flag on the files so that they're no longer included in the daily incrementals, thus preventing those from getting to large. This works out to be ~100GB of files.

* archived files (install kits, videos, etc.) don't get backed up. I keep two copies on separate 1TB external drives stored offline in different locations.
!