Coredumps and swap - was part of Solaris Mem Consumption Post: 302223763

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Operating Systems Solaris Coredumps and swap - was part of Solaris Mem Consumption Post 302223763 by Neo on Monday 11th of August 2008 10:22:36 AM

08-11-2008

Administrator

jlliagre,

You are playing with semantics.

Swap slows you down because it is used instead of RAM..... we don't need to play semantics.

As folks agree, let's move on.

(1) The 2XRAM rule of thump for swap is a legacy artifact from days gone bye bye. RAM is cheap.

(2) There is no compelling reason to use swap if you invest in cheap memory, you will have better performance.

(3) There is no compelling reason to use swap for dump space. If you must dump, you have other choices than swap.

That is all that we have been saying. This is the days of very cheap RAM. Use RAM not swap is what reborg and I have been advising - and in defense of this position of "Use Cheap RAM Not Swap for Better Performance" we were sidetracked with a red-herring argument about dump and swap.

Honestly, you are an unwitting champion of fallacy, (you use a lot fallacy in counterpoint) because you just did the same thing with your statement:

"The default configuration for Solaris is to dump in swap." This sets up another fallacy to many readers that there is something "good" in default configs.

This point is simply another fallacious argument, because there little inherently "good" about default configurations. If so, we should all leave the root password blank, which is also a default configuration in some systems; or leave the IP address 10.0.0.1 (or what ever it is, etc), or we should leave our hostname... etc etc.

My point is a friendly one. You have great technical ideas, and are a strong contributor, but you support your good ideas with logical fallacies. I don't think you mean to do it; but you use fallacy in your counterpoints, and this is something that annoys me when *anyone* does it. Also, it distracts from the core discussion, because we have to deal with fallacies, which defies logic.

If you had of not reacted so strongly with fallacy to reborg's list, but instead commented without a fallacy in your rebuttal, I would have never joined it, as I don't do this as much as I did 10 years ago .... I leave it to the everyday system admin guys like reborg whom personally manages more servers that most could imagine!

In other words, keep up the great work, but learn to see what is fallacy and when you use it in your debate points, and then evolve toward not using fallacious logic or implications. Wikipedia is a great place to learn the basics.

Neo

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LEARN ABOUT X11R4

savecore

savecore(1M)                                              System Administration Commands                                              savecore(1M)

NAME

       savecore - save a crash dump of the operating system

SYNOPSIS

       /usr/bin/savecore [-Lvd] [-f dumpfile] [directory]

DESCRIPTION

       The  savecore  utility saves a crash dump of the kernel (assuming that one was made) and writes a reboot message in the shutdown log. It is
       invoked by the dumpadm service each time the system boots.

       savecore saves the crash dump data in the file directory/vmcore.n and the kernel's namelist in directory/unix.n. The  trailing  .n  in  the
       pathnames is replaced by a number which grows every time savecore is run in that directory.

       Before writing out a crash dump, savecore reads a number from the file directory/minfree. This is the minimum number of kilobytes that must
       remain free on the file system containing directory. If after saving the crash dump the file system containing directory  would  have  less
       free  space the number of kilobytes specified in minfree, the crash dump is not saved. if the minfree file does not exist, savecore assumes
       a minfree value of 1 megabyte.

       The savecore utility also logs a reboot message using facility LOG_AUTH (see syslog(3C)). If the system crashed as a  result  of  a  panic,
       savecore logs the panic string too.

OPTIONS

       The following options are supported:

       -d              Disregard  dump  header valid flag. Force savecore to attempt to save a crash dump even if the header information stored on
                       the dump device indicates the dump has already been saved.

       -f dumpfile     Attempt to save a crash dump from the specified file instead of from the system's current dump device. This option  may  be
                       useful if the information stored on the dump device has been copied to an on-disk file by means of the dd(1M) command.

       -L              Save  a  crash  dump of the live running Solaris system, without actually rebooting or altering the system in any way. This
                       option forces savecore to save a live snapshot of the system to the dump device, and then immediately to retrieve the  data
                       and  to  write it out to a new set of crash dump files in the specified directory. Live system crash dumps can only be per-
                       formed if you have configured your system to have a dedicated dump device using dumpadm(1M).

                       savecore -L does not suspend the system, so the contents of memory continue to change while the dump is saved.  This  means
                       that live crash dumps are not fully self-consistent.

       -v              Verbose. Enables verbose error messages from savecore.

OPERANDS

       The following operands are supported:

       directory               Save  the crash dump files to the specified directory. If directory is not specified, savecore saves the crash dump
                               files to the default savecore directory, configured by dumpadm(1M).

FILES

       directory/vmcore.n

       directory/unix.n

       directory/bounds

       directory/minfree

       /var/crash/'uname -n'           default crash dump directory

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+

SEE ALSO

       adb(1), mdb(1), svcs(1), dd(1M), dumpadm(1M), svcadm(1M), syslog(3C), attributes(5), smf(5)

NOTES

       The system crash dump service is managed by the service management facility, smf(5), under the service identifier:

       svc:/system/dumpadm:default

       Administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed  using  svcadm(1M).  The  ser-
       vice's status can be queried using the svcs(1) command.

       If the dump device is also being used as a swap device, you must run savecore very soon after booting, before the swap space containing the
       crash dump is overwritten by programs currently running.

SunOS 5.10                                                          25 Sep 2004                                                       savecore(1M)

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