How can I create a ramdrive?

[Guy Blatt]

How can I create a ram drive under HP-UX 11? I want to use ram as disk space to increase disk I/O performance. This application needs to think it is writing and reading to/from a disk.

[Patrick Wallek]

According to this TKB document there was no support for a RAM Disk in HP-UX 8.x, 9.x or 10.x so I seriously doubt there is support in 11.

http://us-support.external.hp.com/cki/bin/doc.pl/sid=9ff1a27e0c26d50b68/screen=ckiDisplayDocument?docId=200000024602486

[Bill Hassell]

The ramdisk driver was designed to be used only with a boot/install kernel and is very limited in maximum size. It is undocumented because it is not stable from revision to revision. Changes to the underlying driver are not documented.

The buffer cache will accomplish most of what a ramdisk would provide.

[Wodisch · Accepted solution]

Hello Guy,

in case you still want to know how to do it, the way it
worked some years ago - I have not tried this for quite
some time: ("#" means a comment line)

0) # create a "make_tape_recovery" tape for your box!

1) #Modify your kernel to include the "ram" driver:
1) cd /stand/build
1) /usr/lbin/sysadm/system_prep -v -s system
1) vi /stand/build/system
1) # Edit the system file and add the "ram" driver
1) mk_kernel -s system
1) mv /stand/system /stand/system.good
1) cp /stand/vmunix /stand/vmunix.good
1) rm -rf /stand/vmunix/dlkm.good
1) mv /stand/dlkm /stand/dlkm.good
1) mv /stand/build/system /stand/system
1) kmupdate
1) shutdown -y -r 0

2) # set up the device files and mount the ramdisk:
2) # create the device files with major 9 (both b and c),
2) # and minor 0xVSSSSS, where "V" is the volume num,
2) # and "SSSSS" is the number of sectors in the ram
2) # disk, each sector is 256 bytes.
2) mknod /dev/rram1 c 9 0x101000
2) mknod /dev/ram1 b 9 0x101000 # that's 1MB
2) mkfs -F hfs /dev/rram1 # no point in VxFS here
2) mount /dev/ram1 /ramdisk

As everybody (especially Bill :-) pointed out:
THIS IS UNSUPPORTED, dangerous, and such...

HTH,
Wodisch

[John P. Kole]

I thought the minor number was actually of the form "0xVSSSSX", where:
"V" - is the volume num
"SSSS" - is the number of sectors
"X" - is defined as "bit flags":
0x0 - use a sector size of 1kb.
0x1 - use a secotr size of 64kb.
0x2 - don't use buffer cache.