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

[Craig White]

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, etc.
> > 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 blocks.
> > 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 was.
> 
> 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 SSD).
> 
> 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 needs).
> 
> 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?

Craig