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I know there are a couple of key characteristics that determine the reliability of HDDs, but is there a difference between 2.5" and 3.5" drives?

In the past I've always assumed that 3.5" drives were likely to be more robust...but I am now questioning that because I have absolutely no evidence (let alone a half-baked theory) to back it up.

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Between which 2.5" and 3.5" drives? A questions such as this cannot be answered without context. –  John Gardeniers Mar 8 '11 at 11:41
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Let's just say there is no systematic difference that inherently makes 2,5" drives less reliable than 3,5" drives, both can be considered as equal. But of course there is a difference between a 15K RPM SAS 24x7/RAID drive in 2,5" and a cheap desktop drive in 3,5" :) –  SvW Mar 8 '11 at 11:49
    
Closers: How is this an argumentative topic? <Stumped> @Sven: That's the kind of answer I was looking for....why in a comment? Cheers, though! –  Stu Thompson Mar 8 '11 at 12:03
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4 Answers

up vote 2 down vote accepted

No not really, 2.5 and 3.5 inch drives are mostly the same, including interface and whatnot but 3.5 inch drives are usually faster and larger in space because there is more stuff you can fit into 2.5 vs 3.5 inches. 3.5s are cheaper because of space constrains but usually no more reliable than a 2.5 and vise versa. (in practice)If you could fit a 3.5 drive do it, it'll be cheaper and bigger(storage wise)

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Bigger and cheaper is not everything when it comes to servers. If you run a large database, you would like to have fast access times and use 15K RPM drives, which are always only 2,5", even when in a 3,5" case (this is because the rotational forces get too strong at the outer edge of a 3,5" platter at 15K RPM). Using 2,5" drives then has the advantage that you can fit more drives into the same space. –  SvW Mar 8 '11 at 12:56
    
I've seen performance numbers on HP ProLiant equipment showing transfer rates on 2.5" 10K's to be as fast as 3.5" 15K's. So "usually faster" should be validated with the HD or server vender. –  Bret Fisher Mar 8 '11 at 14:40
    
I tried to stick to generalizations but you both are right –  Jacob Mar 8 '11 at 19:20
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You can't base that just on the form-factor. What's way more important is how the vendor dedicates the hard disk. There are consumer disks with both sizes, which are mainly meant for running just a few hours a day and are lightly loaded.

Enterprise disks (SAS, nearline-SATA) are dedicated for 24/7 usage and higher loads. So if you need reliability, use those.

The most important characteristic to consider when choosing between 3.5" and 2.5" is typically size and energy consumption. If you are tight on both, you should choose 2.5", else you could go with 3.5" which are typically cheaper per GB.

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The real question is what are you you trying to do? If you have a choice between two enclosures, check with the vendor(s) to see what disks are being put in, and see what the warranty period and the manufacturers MTBF on the drives.

Personally, I have seen 2.5" drives fail on me more frequently than 3.5" drives, and I have seen 2.5" drives have 1-3 year warranties versus 3-5 year warranties for 3.5" drives. To be sure, 2.5" drives are more likely to be installed in laptops, which tend to bounce around and have less ventilation.

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Coming from someone who works on computers regularly I would say in my opinion 2.5" drives are crap. They most generally cost more for the same GB and in my experience fail at, at least 3x the rate of the 3.5" drives. Just as an example I have a WD Blue 2.5" not even 1 year old that was never even installed in a laptop and has been sitting in my desktop since day 1. It is now a paper weight. In my same desktop I have a WD 3.5" drive that was made like 4 to 5 years ago, has been moved around from one desktop to another I don't know how many times and it works just as good as the day I got it. The sad part is I don't even like WD but I got a good deal on that Blue drive and was under the impression they are supposed to be reliable. I usually go with Seagate as I have about 10 of their various SATA1 to SATA3 3.5" drives that do nothing all day but serve media files and get accessed constantly while uploading torrents. Just my 2 cents.

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This answer isn't very helpful for systems administrators, who tend to focus on servers. –  mfinni May 26 '13 at 21:47
    
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I'll take your subjective answer and raise you my own - I have a single server with 24x 2.5" drives, and another with 16 2.5" drives and another with 8x 2.5" drives. I have not had a single failure of any of the drives in 2.5 years. –  Mark Henderson May 26 '13 at 21:53
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