Re: measuring swap partition speed

On Fri, Dec 15, 2023 at 08:41:10AM -0700, Warner Losh wrote:

> What's the underlying hardware?

my apologies, I should have supplied this detail initially.
It's a spinning rust TOSHIBA MQ01ABD100

> So the good news, kinda, is that if this is spinning rust, your swap
> partitions are
> on the fastest part of the disk. I'd expect 1 that's 12G would work better
> than 6 that
> are 2G since you'd have less head thrash. Parllelism with multiple swap
> partitions
> works best when they are on separate spindles.

ok that's easily fixable. It was originally one big 12G swapspace.
The reason it's split into 6 is for testing purposes. I've noticed when
swap gets used there's the marked slowdown even if the process using
it has paused. So I've found that using swapoff then swapon puts these
processes back into active memory and the system sluggishness goes,
for a short while until swap gets used again. With the swapspace split,
I can swapoff/on each partition individually. If there's 2GB free mem
and 3GB on swap, I can swapoff a couple of partitions, swapon them again
then swapoff/on the relatively full partition to get total swap use
back to 0.

>The bad news is that your disk may be fine. I'd expect that as the ZFS
>partition fills up,
>the seek size will increase as greater distances have to be traversed to
>get back
>to the swap space. There's a sweet spot of a few tens of GB that drives
>usually can seek
>far faster than longer throws...

(not an SSD)

TYVM for the fio tip. Am building it now.

I'm wondering really if I should reprovision this rpi4 for UFS rather
than zfs. Have had great positive experience with zfs as data (ie, booting
ufs, zfs is a non-bootable single disk or array), less than ideal with
zfs-on-root. There's periodic backups and not much call for this device to
utilise zfs functionality that can't be provided on hardware with more
horsepower.

it must be said though that FreeBSD is *very stable* on this hardware.

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