asterisk users - Apr 2007 - Re: On Topic: Cheapest Asterisk USB Key?

On Mon, 2007-04-02 at 16:30 -0700,
asterisk-users-request@lists.digium.com wrote:
> Date: Mon, 02 Apr 2007 20:26:09 +0100
> From: Thomas Kenyon <digium@sanguinarius.co.uk>
> Subject: [asterisk-users] Re: On Topic: Cheapest Asterisk USB Key?
> To: Asterisk Users Mailing List - Non-Commercial Discussion
>         <asterisk-users@lists.digium.com>
> Message-ID: <461158D1.2020408@sanguinarius.co.uk>
> Content-Type: text/plain; charset=ISO-8859-1
> 
> Salvatore Giudice wrote:
> 
> > You should be aware that flash memory is generally not the best
> medium to
> > store data when you have a high number of read/writes. Flash memory
> will
> > fail much more quickly under these conditions.
> 
> Does this mean that devices such as the samsung Flash SSD (part #
> MCAQE32G5APP-0XA00) and the Supertalent Flashdrives are less reliable
> than the HD equivalents. (since reliability is supposed to be their
> biggest selling points)? 
	What it means is that Flash memory cells wear out after a large number
of read/write cycles, but not nearly as large as hard drives:
http://en.wikipedia.org/wiki/Flash_rom#Limitations . So using Flash in
place of RAM, even when high speed isn't important, can wear out the
Flash - it will probably wear out even before HDs, which live less long
than does RAM. Until the Flash wears out, it is extremely reliable, and
techniques for ensuring it doesn't destroy data as it wears out are
built into the Flash HW (though it will eventually wear out take data
with it).

	But I'm not talking about using the Flash as RAM, just using it for a
low-load persistent store like a HD, where a HD would be overkill in
every way.
-- 

(C) Matthew Rubenstein

On Mon, 2007-04-02 at 22:12 -0400, Matthew Rubenstein wrote:
> 	What it means is that Flash memory cells wear out after a large number
> of read/write cycles, but not nearly as large as hard drives:
> http://en.wikipedia.org/wiki/Flash_rom#Limitations . So using Flash in
> place of RAM, even when high speed isn't important, can wear out the
> Flash - it will probably wear out even before HDs, which live less long
> than does RAM. Until the Flash wears out, it is extremely reliable, and
> techniques for ensuring it doesn't destroy data as it wears out are
> built into the Flash HW (though it will eventually wear out take data
> with it).
> 
> 	But I'm not talking about using the Flash as RAM, just using it for a
> low-load persistent store like a HD, where a HD would be overkill in
> every way.
I thought flash waers out on writing, not reading...
So, keep /tmp,/var/log and its friends on ram-disk, or pass the logging
you don't want to loose via a remote syslog, a remote mysql-server (or
via nfs-mount).
(For running servers I keep /usr and /opt mounted as read-only, to avoid
accidental writing)


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On Mon, 2 Apr 2007, Matthew Rubenstein wrote:
> 	But I'm not talking about using the Flash as RAM, just using it for a
> low-load persistent store like a HD, where a HD would be overkill in
> every way.
I boot my systems off a flash IDE drive. There's a partition with just 
enough of a root filesystem to make lilo work, a /boot directory with a 
kernel image and memtest and an initrd.gz which is a compressed ext2 
filesystem...

It is uncompressed into RAM and then the system runs entirely from RAM. 
There is a small 2nd partition on the device which I keep a tar-file of 
configuration settings. This us untarred once the system boots and fills 
in things like /etc/asterisk, /var/www/docs and a few other config files, 
including /var/spool/asterisk/astdb.

I have a 2nd flash IDE drive for voicemail. This is mouinted as a live 
filesystem and I use GSM only to store voicemail (so a 64MB device is 
going to give me many hours of VM storage).

Seems to work for me and keeps writes back to the important flash device 
(the boot one) to a bare minimum... I force fsck on the voicemail device 
at boot time, if there are any errors and I'm working on a
'sanitiser'
too, which will remove any broken files - so it'll make sure there is a 
.WAV file for every .txt file and so on. I figure losing the occasional 
voicemail might be acceptable after someone pulls the plug on it. (and my 
experiences of this have been good in that I've nver yet lost a file)

Gordon