[CentOS] Odd Question... MAX Ram Disk Size

Scott Heisler scott.heisler at huntleighusa.com
Thu Mar 31 17:26:37 UTC 2005

Thanks everyone for the great INFO... This was EXACTLY what I needed and
had a very hard time finding out.  The mount -t tmpfs -o size=1g none
/ramdisk worked perfectly.  I needed temporary ram space to use as disk
space.  Thanks!

Just to explain further, the "images" are not ISO's... These are hard
drive images, like GHOST files (only using a Linux free application).
But to further explain, even if I mounted an ISO, there would still be
disk IO.. I'm trying to eliminate the disk I/O from the equation so I
can be downloading 20 or 25 machines at the same time.  Since the server
us a dual 2.0gig Xeon and I have gig all the way from the server to the
desktop.. This should scream!

Thanks again. 


-----Original Message-----
From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On
Behalf Of Craig White
Sent: Thursday, March 31, 2005 10:38 AM
To: centos at centos.org
Subject: Re: [CentOS] Odd Question... MAX Ram Disk Size

On Thu, 2005-03-31 at 09:59 -0600, Aleksandar Milivojevic wrote:
> Scott Heisler wrote:
> > I want to put that image file on a RAMDISK on my server.
> > The image file is between 3 and 4 gig.  I have 6 gig in the server, 
> > so plenty of memory.  I modified GRUB to increase the size of my ram

> > disk... First I started with a 200mb, that worked group, formatted,
> > Then I tried 1gig - everything looks like it works but when I mount 
> > it, it tells me the volume is not formatted or has invalid super
> > Perhaps I'm exceeding the allowable built-in ramdisk limit, but I 
> > couldn't find any docs anywhere that would tell me what that limit
> When you say ramdisk, do you mean ramdisk as in ramsdisk device
> (hardware) that keeps information accross system reboots and/or power 
> cycles, or ramdisk as in file system that exists only in your server's

> RAM and is lost each time machine is rebooted?  Not clear from your 
> question.  You mention having "enough RAM for it in server" (which 
> would imply later), but you also say that you are looking for "device"

> (which would imply former).
> If you are looking for self-contained device, there are many solid 
> state disks (SSD) available on the market.  Basically, they look like 
> disk, the "only" difference is instead of having magnetic plates, they

> store information into internal RAM (either battery backed up, or of 
> the non-volatile type).  System sees them as normal IDE/SATA/SCSI/FC 
> drive (depending on the interface), and you don't need to have 
> anything special to access them.  The speed is usually limited by 
> interface used and type of memory used (obviously EEPROM based SSD 
> will have much worse write times then DRAM with battery backup based
> If you are looking for solution to use your server's memory as 
> temporary RAM disk (you don't care information being lost when you 
> reboot or power cycle), something like this works nicely:
> # mount -t tmpfs -o size=8g none /ramdisk
> That would create 8GB memory-based file system.  The memory file 
> system uses is swappable.  So just make sure free RAM + free swap is 
> larger than 8GB, and you should be fine.  Of course, you can create 
> smaller or larger system too.  Basically it is the same thing as tmpfs

> on Solaris systems.  I kind of like to mount /tmp this way (of course,

> with much smaller size, usually 32-128MB, depending on server's
> Or you can place it in fstab to have it always available:
> none   /ramdisk   tmpfs   size=8g   0   0
this is great info and I suppose I might find use for it someday but
wouldn't a loop mount from an iso file (the disk image) be better for
this purpose?


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