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Full Discussion: memcpy error
Top Forums Programming memcpy error Post 302567167 by achenle on Saturday 22nd of October 2011 06:33:42 PM
Old 10-22-2011
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.
 

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LEARN ABOUT CENTOS

scsi-rescan

RESCAN-SCSI-BUS.SH(1)						   User Commands					     RESCAN-SCSI-BUS.SH(1)

NAME

       rescan-scsi-bus.sh - script for adding and removing SCSI devices without rebooting

SYNOPSIS

       rescan-scsi-bus.sh [options] [host [host ...]]

OPTIONS

       -a, --alltargets
	      scan all targets, not just currently existing [default: disabled]

       -d     enable debug			 [default: 0]

       -l     activates scanning for LUNs 0--7	 [default: 0]

       -L NUM activates scanning for LUNs 0--NUM [default: 0]

       -w, --wide
	      scan for target device IDs 0--15	 [default: 0--7]

       -c     enables scanning of channels 0 1	 [default: 0 / all detected ones]

       -r, --remove
	      enables removing of devices	 [default: disabled]

       -f, --flush
	      flush failed multipath devices	 [default: disabled]

       -i, --issue-lip
	      issue a FibreChannel LIP reset	 [default: disabled]

       -u, --update
	      look for existing disks that have been remapped

       -s, --resize
	      look for resized disks and reload associated multipath devices, if applicable

       --forcerescan
	      rescan existing devices

       --forceremove
	      remove and readd every device (DANGEROUS)

       --nooptscan
	      don't stop looking for LUNs is 0 is not found

       --color
	      use coloured prefixes OLD/NEW/DEL

       --hosts=LIST
	      scan only host(s) in LIST

       --channels=LIST
	      scan only channel(s) in LIST

       --ids=LIST
	      scan only target ID(s) in LIST

       --luns=LIST
	      scan only lun(s) in LIST

       --sync, --nosync
	      issue a sync / no sync [default: sync if remove]

       --attachpq3
	      tell kernel to attach sg to LUN 0 that reports PQ=3

       --reportlun2
	      tell kernel to try REPORT_LUN even on SCSI2 devices

       --largelun
	      tell kernel to support LUNs > 7 even on SCSI2 devs

       --sparselun
	      tell kernel to support sparse LUN numbering

	      Host numbers may thus be specified either directly on cmd line (deprecated) or or with the --hosts=LIST parameter (recommended).

       LIST: A[-B][,C[-D]]... is a comma separated list of single values and ranges (No spaces allowed.)

SEE ALSO

       rescan-scsi-bus.sh Homepage: http://www.garloff.de/kurt/linux/#rescan-scsi

       sg3_utils Homepage: http://sg.danny.cz/sg

rescan-scsi-bus.sh 1.57 					    leden 2014						     RESCAN-SCSI-BUS.SH(1)
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