Juve said:
I've bought an external enclosure for my 160 Gb harddisk. It doesn't
have a fan, but it is built in such a way that air flow through the
enclosure. Is that enough?
The only way to find out for sure is by measuring the temperature of
the HDD under worst-case conditions (hot room, lots of head seeking)
and by comparing that against the maximum allowed temperature
(probably 55-60C) and the temperature of a similar HD (same diameter
platters, same RPMs) that's in a well-ventilated enclosure or
computer. Or compare the enclosure to the enclosure used for an HDD
(again, same diameter platters, same RPMs) that's warranted for 5
years by the manufacturer. Look for vent holes arranged not only so
the air will flow both in and out but also flow all over the HDD
(i.e., in from the front bottom, out the top rear).
Should I be worried about overheating?
Considering the poor quality of computer accessories, yes, but don't
obsess over it the way some people obsess over CPU temperature or
performance benchmarks.
Here's an example of a bad enclosure, called a Neo:
http://farm4.static.flickr.com/3285/3145996783_8608688800_o.jpg
It has a cooling fan but so few vent holes in front that it's noisier
when the cover is installed than when it's left off, and I'm including
the noise of the HDD. The HDD sits almost flush with the bottom, so
the drive electronics get almost no air flow (if your enclosure is
similar in this respect, see if you can place some nylon washers
between the drive and enclosure bottom; longer screws may be needed),
and one buyer's HDD burned out a chip, which left a scorch mark in the
enclosure. The seller, Dealsonic, not only gave him a complete refund
but also replaced his internal HDD. But worse than the heat is the
electrical safety: the power supply is internal and is not UL
approved (contrary to what the Dealsonic website originally said), and
normally sits right below the IDE-USB interface card (swung to the
left for visibility), separated only by a thin layer of tough
plastic. Apparently this power supply has no protection against
overvoltage or overcurrent (except a fuse).
In comparison, look at this much better made Bytecc/Welland enclosure:
http://farm4.static.flickr.com/3134/3146880058_fa00cd3486_o.jpg
It too has an internal power supply, but notice that it's housed in a
metal cage and is UL approved. Also the HDD sits about 0.1" - 0.25"
above the bottom, and you can see tiny vent holes around the
indentations for the screws that attach to the HDD.
BTW, external power supplies for enclosures are almost always UL
approved for safety, so I would strongly prefer them over internal
ones.
Does a bigger HDD generate more heat than a smaller one?
The drive capacity has nothing to do with it, except when higher
capacity means more platters. But more important are the diameter of
the platters and the rotational speed. Drives with 2.5" platters run
stone cold unless placed inside a laptop or unventilated enclosure.
Among drives with 3.5" platters, the 7200 RPM models run pretty hot,
but the 5400 RPM ones get only lukewarm. The difference in the amount
of power between the latter is only about 3-4 watts, indicating that
it takes just a little extra power to raise the temperature
considerably. A power supply inside an enclosure will add roughly the
same amount of power -- another reason to prefer external power
supplies.
Some enclosures are claimed to provide adequate cooling solely through
conduction. That may be true for 2.5" HDDs, but I have doubts about
this for 3.5" HDDs (but I'm no expert). And some enclosure makers or
dealers may lie about the conduction cooling. For example, Buffalo
says that the USB 160GB HDD I have is cooled by conduction, even
though its enclosure is made of thin steel (steel conducts heat
roughly 10x worse than aluminum does) and the internal HDD makes
contact with the enclosure at just three small spots. I'm not even
sure that my Western Digital 3.5" Elements USB drive is cooled
adequately, despite the enclosure being made of fairly thick
aluminum. Considering that data recovery costs a lot, lot more than
any enclosure, I often drill extra vent holes in my enclosures (remove
the internal drive first, and be sure to remove all the metal chips
and powder from the drilling and any burrs that may short against the
electronics).
FatWallet.com's really long, really thorough thread about external
drive enclosures:
http://www.fatwallet.com/forums/arcmessageview.php?catid=28&threadid=496281