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I'm planning to buy a NAS (network attached storage) box and I've picked the Synology DS209. I want to set up a RAID 1 array and I'm wondering if I should buy a matching pair of hard drives or if it would be better to buy from different manufacturers. I'm concerned that a matching pair would be more likely to fail at the same time.

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up vote 5 down vote accepted

A general rule-of-thumb is to have matching disks in the array. The characteristics of each manufacture will differ, so the more similar the disks, the less like the RAID controller will have to deal with data corruption. That said, you don't have to use matched disks. For instance, make sure you replace a failed disk with another the same size or larger.

I wouldn't be concerned with 2 drives from the same manufacturer dying at the same time. The odds of that happening are tremendous -- probably equal to that of 2 drives from different manufacturers dying at the same time.

Now, if you're worried about protecting your data, please make sure that you don't solely rely on your RAID1 array. It is not a backup solution! Make sure you backup your important data, take it offline, and take it offsite.

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Thanks for the response. So hard drive quality has reached the point where I shouldn't be concerned about manufacturing/firmware defects affecting a "batch" of drives? I do plan to back up to an external USB drive and store it offsite. – Jamie Ide Jul 16 '09 at 14:17
I don't think the hard drive manufacturing process is perfect, so there are always going to be cases of "defects" in drives. Sure, these defects can often affect a batch of drives from one manufacturer, but the chances of those defects causing a failure at the same exact time are not likely. It's important to monitor the status of your array for this reason. If you discover a defective drive, get it replaced immediately! – Russ Warren Jul 16 '09 at 14:24
I'd recommend reading this: about drive reliability. Basically, the harder you use a drive the more likely it is to fail, but you shouldn't worry about it too much. It does happen sometimes that people have problems like with IBM Deskstars (Deathstars) that I had 4 of that worked happily for over 5 years, but people said were unreliable. – Joshua Nurczyk Jul 16 '09 at 14:28
I agree with the original answer, drives are pretty reliable now. But those IBM Deskstars were a well documented disaster, there's a reason Hitatchi bought IBM's drive unit. At least they readily replaced them under the warranty. – Auxonic Aug 6 '09 at 12:43

Go ahead and buy from the same manufacturer, the chance that they would fail at the same time just because of that is highly unlikely. There is also a risk that one of the drives is slower, meaning that the faster drive will have to adapt to the slower one.

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Tell that to an IBM 75GXP owner ^^ I lost both drives in a RAID-1 in two consecutive days, too bad I didn't have a spare at home. – Shadok Nov 21 '12 at 17:16

I've actually experienced two drives from the same manufacturer crashing at the same time. It's extremely rare though, but I'd still consider getting different drives on my next storage solution, or go for some higher reliability drives (if such a thing really exists).

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