"Readyboost for Linux," take two?

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GJones
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"Readyboost for Linux," take two?

Post by GJones » 29. Aug 2013, 04:27

Or the next best thing, anyway: putting the root filesystem's journal on a flash device. After stumbling across a blog entry on external journals, I decided to try this on Salix. ATM I have Salix 14.0.1 KDE running on my netbook, with JFS and an external journal.

Is it faster?

... Not really.

At first I tried putting the journal on a MicroSD card, and found that KDE took maybe 50% longer to start than with an internal journal. So I tried moving it to a somewhat faster USB stick... But it was still relatively slow. Suffice to say I am not impressed.

I also tried using ext4 with an external journal on my headless laptop... That was a failure, the kernel panicked on boot. I suspect that unlike JFS it needs a /boot partition. Actually I probably should have used one with JFS, come to think of it.

I'll see if I can I can improve the performance situation. My guess is that it's due to the physical nature of USB media, and not really fixable, but it can't hurt to experiment a bit.

GJones
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Re: "Readyboost for Linux," take two?

Post by GJones » 29. Aug 2013, 10:45

Hah, success!

Tried again, this time with Mageia and ext4. I used separate root and home partitions, and put the journals in separate 256 MB partitions on a 16 GB SD card. (The rest of the card I formated FAT32, for backup space.) I'm thinking maybe excessively large journal volumes create some kind of overhead?

Anyway it doesn't make things that much faster, but it certainly doesn't make things slower. I suspect performance may be improved during heavy I/O though, since there would be fewer write requests to the hard disk.

Only one problem so far: the SD card is slow to appear in /dev, so systemd drops me to a command shell, and I have to exit the shell manually to continue booting. This should be solvable by adding a 2-second delay before mounting the root partition, but the rootdelay parameter doesn't seem to work for some reason... Anyway I will post a howto once I figure this out.

GJones
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Re: "Readyboost for Linux," take two?

Post by GJones » 3. Sep 2013, 05:09

Interesting - when using an SD card for external journaling, a smaller journal size seems to produce better performance. I would expect the opposite, as is the case on HDDs.

As for the boot delay, that can be done on most distros by using the rootdelay flag, e.g. 'rootdelay=3' for a 3 second delay before mounting the root FS - 3 seconds is sufficient for my netbook. Distros that use dracut initrds unfortunately ignore rootdelay, but Salix doesn't have that problem. :)

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sqlpython
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Re: "Readyboost for Linux," take two?

Post by sqlpython » 9. Sep 2013, 21:30

My experience, having used SSDs for over 10 years is as they get full performance degragates..
So, larger partitions being slower doesn't surprise me.
Debian ( Stretch 9, Sid ) Salix OpenBox 14.1, Gentoo, Calculate

GJones
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Re: "Readyboost for Linux," take two?

Post by GJones » 10. Sep 2013, 22:09

Really? Interesting; if the performance degrades as they fill up, I would expect a smaller (and thus more quickly filled) journal partition to produce worse performance...

Oh, I should mention that ext4 users should turn on journal_async_commit. This should help flash drive lifespan, and definitely helps performance.

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