12-16-2008
SAP swap recommendations
Hello all.
My company is installing an SAP ERP financials. The consultants are asking me to allocate 30Gbytes of swap. This is on a dedicated Linux box running Redhat 5 64Bit OS. It has 16GB of RAM.I have asked for an explanation but all I'm getting is that this is what SAP recommends. It seems really strange. Redhat recommends 1/3 times RAM for swap on RHEL5. I am seeing virtually no swapping going on. It seems to me if they need this much swap I should be adding RAM. My experience from way back it that too much swap on a linux box can cause problems. This was back in 2002 or so but I'm sure we were seeing really bad performance with too much swap that went away once we reduced it to 2GB of swap only.
My question is simple. Anyone out there running SAP with less swap than RAM? If so, are you experiencing and real problems?
Thanks.
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LEARN ABOUT REDHAT
swapoff
SWAPON(8) Linux Programmer's Manual SWAPON(8)
NAME
swapon, swapoff - enable/disable devices and files for paging and swapping
SYNOPSIS
/sbin/swapon [-h -V]
/sbin/swapon -a [-v] [-e]
/sbin/swapon [-v] [-p priority] specialfile ...
/sbin/swapon [-s]
/sbin/swapoff [-h -V]
/sbin/swapoff -a
/sbin/swapoff specialfile ...
DESCRIPTION
Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user
initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several
devices and files.
Normally, the first form is used:
-h Provide help
-V Display version
-s Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25.
-a All devices marked as ``swap'' swap devices in /etc/fstab are made available. Devices that are already running as swap are silently
skipped.
-e When -a is used with swapon, -e makes swapon silently skip devices that do not exist.
-p priority
Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel.
priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field
of /etc/fstab for use with swapon -a.
Swapoff disables swapping on the specified devices and files. When the -a flag is given, swapping is disabled on all known swap devices
and files (as found in /proc/swaps or /etc/fstab).
NOTE
You should not use swapon on a file with holes. Swap over NFS may not work.
SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8)
FILES
/dev/hd?? standard paging devices
/dev/sd?? standard (SCSI) paging devices
/etc/fstab ascii filesystem description table
HISTORY
The swapon command appeared in 4.0BSD.
Linux 1.x 25 September 1995 SWAPON(8)