Re: [gentoo-user] Swap performance

[Volker Armin Hemmann <volkerarmin@googlemail.com>]

On Wednesday 25 May 2011 10:31:19 Paul Hartman wrote:

> When I move the swap to a slow SD card instead (2MB/sec transfer
> rate), even in that slow device, swapoff on the eMMC swap partition
> with ~500M in-use takes about 2 or 3 minutes at most with the data
> being swapped slowly into the SD card.
> 
> So I think in your case it should be much faster than that!

you are comparing apples with oranges (harddisks with moving arms with solid 
state devices).

Do yourself a favour. Look up how long a harddisk needs to position its head.

Now you can calculate how many times a second a harddisk can position its 
head.

Now remember: swap is stupid, so lots and lots of head movement needed (and a 
cash flush is running too - so even more movements to write all that crap to 
disk),

The result: the whole mess is fscking slow.

You can have a nice fat raid with nice and fast harddisks - if you try to 
stream to a 15 year old DLT drive with 5/10mb/sec speed the dlt drive will 
constantly rewind - because harddisks suck when they have to seek. And swap 
(just like a backup) = lots and lots and lots of seeks.