ReadyBoost Technology for Ubuntu and Linux

[Oystein Viggen]

* [Florian Zeitz] 

> Linux has been able to do this for ages, but it has been considered a
> bad idea, because it wears the memory sticks flash.
> In theory all it takes is:
> 1. # mkswap /dev/sdX (where sdX is your memory stick)
> 2. Edit your fstab to say:
> /dev/sdX none swap sw,pri=2 0 0
> UUID=stuff none swap sw,pri=1 0 0
> instead of
> UUID=stuff none swap sw 0 0
> 3. # swapon -a

Then again, this is nothing at all like ReadyBoost.

What ReadyBoost apparently does is to use the flash drive as a secondary
disk cache (note: disk cache, not swap) for often read, rarely written
data.  The point being that while the disk can deliver 50MBps and the
flash drive can only deliver maybe 20MBps, you still read a 4k block of
data faster from the flash drive because the much lower seek time makes
up for the lower sustained data rate.

Of course, the most read data will be present in the disk cache in RAM
anyway, so ReadyBoost only provides an advantage for not-quite-as-often
read data, or maybe during boot.  It is also quite clearly more
beneficial (except maybe during boot) to add the same amount of RAM
instead of ReadyBoost flash drive to your system, but 2GB flash drive is
cheaper than 2GB RAM.

There's also little reason to think that this needs to wear out the
flash drive very quickly.  If you store system files (or more correctly,
blocks from system files) like the contents of /bin, /lib, /etc, and
most of /usr, these are files that hardly ever change (except during
dist-upgrade or the occasional security update), but still represent a
lot of small reads and would as such benefit from being read from a 1ms
seek time flash drive instead of a 10ms seek time hard drive.

To answer the original question, I've not heard of anything like
ReadyBoost for Linux.  Googling for it, I mostly find explanations from
people who did not understand ReadyBoost, and present solutions like the
one I quoted.

Øystein
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