[WYLUG-help] "lost" hdd

[Roger Leigh]

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John Hodrien <johnh at comp.leeds.ac.uk> writes:

> On Sun, 29 Jan 2006, Dave Fisher wrote:
>
>> I'm not sure of the situation with current filesystems and disk
>> hardware, but historically, dedicated swap partitions performed much
>> better than swap _files_ (i.e. files stored on a normal filesystem).
>
> AFAIK in the past you couldn't even have a swap file.  I don't think
> there's a performance difference anymore, since I was under the
> impression that a swap file still had to be contiguous on disk.

With current 2.6 kernels, a swap partition and swap file have
identical performance characteristics.  The file need not be
contiguous (the filesystem can't ever make that guarantee), but it
must not be sparse.  This is because after the initial swapon(2) it
does not go via the VFS layer, but straight through the page
cache/block layer, AFAICT.

> I'd never consider swap as having any performance.  Apart from the
> value of swapping out bits that effectively never get used, you
> never actually *want* to use swap.

That depends on whether or not you want to use it for things other
than dirty pages.  tmpfs can make good use of swap, which is why I
have 6 GiB of swap on the system on which I'm writing this message.


Regards,
Roger

- -- 
Roger Leigh
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