SD card unpartitioned space -- used for swap?

[C. Scott Ananian]

On Mon, Nov 22, 2010 at 2:21 PM, Mikus Grinbergs <mikus at bga.com> wrote:
>> Downsides
>> - Increased SD card wear
>
> For about two years now, I've been defining a swap partition on the
> (external) "permanent" SD card I use with my XO-1 systems.  So far, I
> have never experienced any problems with that setup.

A couple of points:
a) wear lifetime is statistical, so one report does not equal a guarantee
b) wear lifetime is roughly proportional to SD card size, so if you're
using a largish card your report is not applicable to smallish card
users (you didn't say how large your card was)
c) life expectancy of the XO-1 is 5 years (you provided a report after 2)

It's not too hard to actually write enough to an SD card to wear it
out.  For one 4GB card I tested, about 5TB of writes is enough; wad's
got equivalent numbers for all of the flash technologies OLPC has
tested.  To advance the discussion, collecting a quantitative measure
of "average swap writes per day" given some usage profile would let
you more-or-less rigorously determine whether swap was 'safe' over the
5 year expected lifetime of the device.  If you started
collecting/recording total data written to your swap partition, I'd be
very interested to hear (in a month or so) what your numbers were.
  --scott



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