10-24-2011
Quote:
Originally Posted by
achenle
Hmm, I wonder what happens if you try to read a few GB from a SAN-based file system built on 4 or 6 or maybe more parallel LUNs configured by someone who knows how to lay out storage, and attached with 8 gbps fiber?
Do you really think the VM manager in your kernel can keep up with data coming in that fast?
Guess what? It can't.
Heck, I've seen well-designed 2 gbps SANs with just a few LUNs overwhelm VM managers.
In other words, YES, there ARE reasons to memset() a chunk of RAM *before* you use it.
And that's not even addressing the default Linux method of allowing oversubscription of virtual mamory in the hope that it won't all be used. If reliability and deterministic behavoir are important to you, you don't rely on hope and things like the Linux OOM killer are crazy-bad.
I'm not sure what you're getting at here.... Are you saying the reason to call memset is to assist the VMM in keeping up with a fast transfer?
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LEARN ABOUT DEBIAN
rescan-scsi-bus
RESCAN-SCSI-BUS.SH(8) System Manager's Manual RESCAN-SCSI-BUS.SH(8)
NAME
rescan-scsi-bus.sh - rescan the SCSI bus.
SYNOPSIS
rescan-scsi-bus.sh [ -l ] [ -w ] [ -c ] [ -r ] [ host... ]
DESCRIPTION
rescan-scsi-bus.sh is a program that is used to rescan the SCSI bus using the SCSI add-single-device feature of the Linux SCSI layer.
OPTIONS
-l Activates scanning for LUNs 0 .. 7 (default: 0).
-L NUM Activates scanning for LUNs 0 .. LUN (default: 0).
--luns=LIST
Scan only LUNs in LIST.
-w Enables scanning for device IDs 0 .. 15 (default: 0 .. 7).
--ids=LIST
Scan only device IDs in LIST.
-i, --issue-lip
Issue a FibreChannel LIP reset (default: disabled).
-r, --remove
Enables removing of devices (default: disabled).
--forceremove
Remove and readd every device (dangerous).
-c Enables scanning of channels 0 1 (default: 0).
--channels=LIST
Scan only channels in LIST.
host, --hosts=LIST
If host adapters are given, only these are scanned (default: all).
--nooptscan
Don't stop looking for LUNs if 0 is not found.
--color
Use coloured prefixes OLD/NEW/DEL.
LIST is a comma separated list of single values and ranges (no spaces allowed), e.g. 0,2-3,8,10-15.
AUTHOR
rescan-scsi-bus.sh was written by Kurt Garloff <garloff@suse.de>.
COPYRIGHT
This program is free software. You can use it under the terms of the GNU GPL (General Public License) Version 2 (or any later version, at
your option). Note, that the GNU GPL implies, that there is NO WARRANTY at all. Full text of the GPL can be found in /usr/share/common-
licenses/GPL file.
AVAILABILITY
rescan-scsi-bus.sh is available from
http://www.garloff.de/kurt/linux/scsidev/
March 1998 RESCAN-SCSI-BUS.SH(8)