[solved] USB stick as cache

nTia89 · 2013-08-16 11:41:54

hi fellows,

I have an unused but not too old (at least compared with my hardware on signature )
and I would know if I can use it as a cache (à-la readyboost of W)

or better: first, I should know if this operation make sense, with my combination of hardware (I think through benchmark)
then I could "build" this equipment

thanks

Last edited by nTia89 (2013-08-17 11:51:37)

Trilby · 2013-08-16 11:45:48

USB sticks tend to be terribly slow I/O. While the flash memory itself is certainly fast, the usb is a bottleneck. In most cases I/O to a usb flash drive will be slower than to an internal hard drive. If this is the case here, I don't see how it would be useful as a cache.

EDIT: perhaps there is some other way of using unformatted usb sticks more directly that would side-step this - so I could be wrong. I'm speaking only from experience with writing blocks of data to partitioned usb flash drives which is always *much* slower than saving it to the harddisk.

Last edited by Trilby (2013-08-16 11:47:50)

phanisvara · 2013-08-16 12:42:27

i know that USB sticks' life time is limited to a certain no. of write opreations. using one as cache would probably condemn it to an early grave

nTia89 · 2013-08-16 12:46:55

phanisvara wrote:

i know that USB sticks' life time is limited to a certain no. of write opreations. using one as cache would probably condemn it to an early grave

yes, I know it

but in my case the USB is unused and will remain in that status....

alphaniner · 2013-08-16 13:05:47

Windows did exactly this with ReadyBoost. Looking into it would probably be worthwhile.

Max-P · 2013-08-16 18:02:29

Like already said, USB sticks are usually very slow and would actually slow things down more than anything else unless you have a super-fast 32 GB USB3 drive.

You should test it before actually setting everything up.

Here are some samples from my computer:

max-p ~ % sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 624 MB in  3.00 seconds = 207.94 MB/sec
max-p ~ % sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads: 344 MB in  3.00 seconds = 114.62 MB/sec

max-p ~ % sudo hdparm -t /dev/sdc    

/dev/sdc:
 Timing buffered disk reads:  52 MB in  3.03 seconds =  17.15 MB/sec

sda is an SSD
sdb is a 7200 RPM HDD
sdc is a 16GB USB stick.

You can use dd to write stuff to it and see how fast it went, I'm not doing it on mine because I have data on it, but it's around 3 Mb/s write speed, this is way worse than the HDD.

Unless you have a corner case where you need a lot of random-access over sequential read, it's probably not worth it at all. Your USB stick has to be at least faster than your disk if you want benefits of doing that.

From what I read, Windows uses this for random-access on small files. Linux already use RAM as a cache, so it would make more sense to me to use zram to increase the ram capacity so you can have more data on RAM for ultra-fast access instead of messing around with USB sticks.

Anway, what you want is probably bcache. Have fun.

arcon · 2013-08-16 19:53:29

I am not sure about this but, you can create Swap File in your usb and you can use it for suspending your system.

nTia89 · 2013-08-16 20:41:12

Max-P wrote:

Like already said, USB sticks are usually very slow and would actually slow things down more than anything else unless you have a super-fast 32 GB USB3 drive.
You should test it before actually setting everything up.
Here are some samples from my computer:
max-p ~ % sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 624 MB in  3.00 seconds = 207.94 MB/sec
max-p ~ % sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads: 344 MB in  3.00 seconds = 114.62 MB/sec

max-p ~ % sudo hdparm -t /dev/sdc    

/dev/sdc:
 Timing buffered disk reads:  52 MB in  3.03 seconds =  17.15 MB/sec
sda is an SSD
sdb is a 7200 RPM HDD
sdc is a 16GB USB stick.
You can use dd to write stuff to it and see how fast it went, I'm not doing it on mine because I have data on it, but it's around 3 Mb/s write speed, this is way worse than the HDD.

Unless you have a corner case where you need a lot of random-access over sequential read, it's probably not worth it at all. Your USB stick has to be at least faster than your disk if you want benefits of doing that.
From what I read, Windows uses this for random-access on small files. Linux already use RAM as a cache, so it would make more sense to me to use zram to increase the ram capacity so you can have more data on RAM for ultra-fast access instead of messing around with USB sticks.

Anway, what you want is probably bcache. Have fun.

thank you for your super-comprehensive reply. I'll test my system as soon as I can

decant swap partition on usb could be a good idea too

nTia89 · 2013-08-17 11:51:23

my hd :

[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 200 MB in  3.02 seconds =  66.23 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 204 MB in  3.04 seconds =  67.08 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 200 MB in  3.03 seconds =  66.07 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 204 MB in  3.03 seconds =  67.37 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 200 MB in  3.01 seconds =  66.54 MB/sec

instead, my usb:

[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads:  50 MB in  3.01 seconds =  16.62 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads:  50 MB in  3.00 seconds =  16.65 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads:  52 MB in  3.12 seconds =  16.69 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads:  52 MB in  3.12 seconds =  16.67 MB/sec
[mattia@arch-dekstop ~]$ sudo hdparm -t /dev/sdb

/dev/sdb:
 Timing buffered disk reads:  52 MB in  3.12 seconds =  16.68 MB/sec

this close the problem....

Arch Linux

#1 2013-08-16 11:41:54

[solved] USB stick as cache

#2 2013-08-16 11:45:48

Re: [solved] USB stick as cache

#3 2013-08-16 12:42:27

Re: [solved] USB stick as cache

#4 2013-08-16 12:46:55

Re: [solved] USB stick as cache

#5 2013-08-16 13:05:47

Re: [solved] USB stick as cache

#6 2013-08-16 18:02:29

Re: [solved] USB stick as cache

#7 2013-08-16 19:53:29

Re: [solved] USB stick as cache

#8 2013-08-16 20:41:12

Re: [solved] USB stick as cache

#9 2013-08-17 11:51:23

Re: [solved] USB stick as cache

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