RAM disk.

[Don Lewis]

In article <1223 at tardis.Tymnet.COM> jms at tardis.Tymnet.COM (Joe Smith) writes:
>I understand the joke, but did you know that Sun has done the opposite?
>They have put the ram disk on the swap/paging area.  Actually, it's more
>like any page of physical memory can be used for either a swapped-in page
>or a tmpfs file system page, first come first served.
>
>Small files stay completely in ram.  Large file spill over into swap space,
>but it's still faster than a regular file partition due to not waiting for
>synchronized writes to the directory blocks, the bitmap/freelist, superblock,
>etc.  It's good for /tmp (but not /usr/tmp unless you have a giant swap space.)

Does anyone have a feel for the relative performance of Sun's tmpfs versus
a 4.2 filesystem?  I have an application that uses a lot of temporary
file space.  After it is finished thrashing about with the scratch files
it builds a large data structure in memory.  The amount of swap space
and the amount of scratch file space consumed at one time are someone
complementary.  Without using tmpfs, I need both big swap and big /tmp.
I am interested in combining these into one large swap and using tmpfs.
The issue is what is the performance when simultaneously reading and
writing several large files (and possibly significant paging as well)
using tmpfs versus the same operations using the 4.2 filesystem.  The
hosts in question currently have /tmp and swap on separate drives and
have a fair amount of RAM.
--
Don "Truck" Lewis                      Harris Semiconductor
Internet:  del at mlb.semi.harris.com     PO Box 883   MS 62A-028
Phone:     (407) 729-5205              Melbourne, FL  32901