[mdlug] supplemental memory?

[Michael Mikowski]

Exactly.

SATA disk will be faster than USB2 memory devices for sequential writes (e.g. larger files).  This is guaranteed due the speed advantage the SATA has over USB2.

Now for random reads, seek time is much lower with memory cards, typically 1ms vs 10ms.  So putting swap on a USB stick will either improve your performance (if the disk is making many small reads), or hurt it.   Given the way Linux pages to swap to the disk, I would put odds on the latter.

Now if you want the best of both worlds, buy a SATA interface memory devices; they are called SSD's.  Last I looked, 256GB ran around ~$800.  But great for database servers.

Cheers, Mike  



----- Original Message ----
From: Robert Citek <robert.citek at gmail.com>
To: MDLUG's Main discussion list <mdlug at mdlug.org>
Sent: Tue, March 23, 2010 8:27:11 AM
Subject: Re: [mdlug] supplemental memory?

On Tue, Mar 23, 2010 at 10:55 AM, Jeff Hanson <jhansonxi at gmail.com> wrote:
> They are memory.  FLASH memory is faster than hard drives and much
> slower than RAM but with a limited write cycle life.

I had always thought that flash would be faster than a hard drive
until I did a write test on a USB stick:

$ wtest () { dd if=/dev/zero of=zeros bs=1M count=$1 ; sync ; } ; sync
; time -p wtest 100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 7.38919 s, 14.2 MB/s
real 20.27
user 0.00
sys 0.63

The write same on my internal harddrive:

$ wtest () { dd if=/dev/zero of=zeros bs=1M count=$1 ; sync ; } ; sync
; time -p wtest 100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 1.68022 s, 62.4 MB/s
real 3.90
user 0.00
sys 0.63

The hard drive is about 5x faster.  Fairly consistent over multiple tests, too.

Regards,
- Robert
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