Re: linux raid vs hw raid

Date	2011-04-14 09:15 +0200
From	David Brown <david@westcontrol.removethisbit.com>
Newsgroups	comp.os.linux.misc
Subject	Re: linux raid vs hw raid
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On 14/04/2011 05:42, Grant wrote:
> On Wed, 13 Apr 2011 09:45:58 +0200, David Brown<david@westcontrol.removethisbit.com>  wrote:
>
>> On 12/04/2011 22:13, The Natural Philosopher wrote:
>>> Keith Keller wrote:
>>>> The
>>>> kernel will move things to swap if it hasn't been used in a while and
>>>> free memory is wanted; when the memory frees up, it can leave that data
>>>> in swap so that it can use more physical memory for other tasks (e.g.,
>>>> more disk buffers).
>>>
>>> That is key, It means the rarely used admin processes that ar
>>> essentially asleep, do not fill the RAM.
>>
>> Such processes are usually small, but it's a good principle none the less.
>>
>>
>> The reason I like swap space is as a backing store for tmpfs
>> filesystems.  I usually put /tmp and /var/tmp on tmpfs, and sometimes
>> have additional tmpfs mounts for odd purposes (such as the build
>> directories for large compilations - though obviously that's more
>> desktop than server usage).  Tmpfs is much faster and more efficient
>> than any other filesystem, even if the data is stored on a disk rather
>> than in memory, because it does not give the slightest care to data
>> reliability.
>
> Wonder if you could show your relevant /etc/fstab lines?  I'm curious
> how other do this?

Putting /tmp on tmpfs is not rocket science - if you thought I had some 
cunning secret here, I have to disappoint you :

tmpfs /tmp tmpfs defaults 0 0
tmpfs /var/tmp tmpfs defaults 0 0

(Note that /var/tmp should really survive a reboot.  However, I have 
never heard of any programs that actually rely on that - but no 
guarantees.  /tmp should always be safe on tmpfs.)

You can make a new tmpfs on another directory:

mkdir t
mount -t tmpfs tmpfs t

By default, tmpfs mounts are limited in size to half your physical ram - 
but you can change that with the "size" mount option.  tmpfs takes 
negligible space overhead - you only use ram/swap for the files stored 
there.

>>
>> The Linux kernel is good at memory management, and at balancing what
>> goes in ram and what goes in swap.  Clearly you are always faster with
>> x+y ram instead of x ram and y swap, but x+y ram and y swap is even better.
>
> Grant.

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Thread

linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-05 19:39 -0700
  Re: linux raid vs hw raid Tim Watts <tw@dionic.net> - 2011-04-06 08:01 +0100
    Re: linux raid vs hw raid David Brown <david@westcontrol.removethisbit.com> - 2011-04-06 10:03 +0200
      Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-06 14:00 -0700
        Re: linux raid vs hw raid David Brown <david.brown@removethis.hesbynett.no> - 2011-04-06 23:42 +0200
        Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-08 10:45 +1000
          Re: linux raid vs hw raid David Brown <david@westcontrol.removethisbit.com> - 2011-04-08 11:12 +0200
            Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-08 08:22 -0700
              Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-09 09:51 +1000
                Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-08 17:10 -0700
                Re: linux raid vs hw raid David Brown <david.brown@removethis.hesbynett.no> - 2011-04-09 13:14 +0200
            Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-09 09:47 +1000
              Re: linux raid vs hw raid David Brown <david.brown@removethis.hesbynett.no> - 2011-04-09 13:55 +0200
          Re: linux raid vs hw raid Tris Orendorff <triso@remove-me.cogeco.ca> - 2011-04-12 18:04 +0000
            Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-12 11:34 -0700
              Re: linux raid vs hw raid The Natural Philosopher <tnp@invalid.invalid> - 2011-04-12 21:13 +0100
                Re: linux raid vs hw raid David Brown <david@westcontrol.removethisbit.com> - 2011-04-13 09:45 +0200
                Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-14 13:42 +1000
                Re: linux raid vs hw raid David Brown <david@westcontrol.removethisbit.com> - 2011-04-14 09:15 +0200
                Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-15 08:03 +1000
                Re: linux raid vs hw raid Tim Watts <tw@dionic.net> - 2011-04-15 07:22 +0100
                Re: linux raid vs hw raid David Brown <david@westcontrol.removethisbit.com> - 2011-04-15 09:28 +0200
                Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-19 11:20 +1000
              Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-14 13:38 +1000
                Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-13 21:49 -0700
            Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-14 13:34 +1000
              Re: linux raid vs hw raid Tris Orendorff <triso@remove-me.cogeco.ca> - 2011-04-15 21:59 +0000
                Re: linux raid vs hw raid "Peter J. Holzer" <hjp-usenet2@hjp.at> - 2011-04-16 00:56 +0200
                Re: linux raid vs hw raid The Natural Philosopher <tnp@invalid.invalid> - 2011-04-16 01:32 +0100
  Re: linux raid vs hw raid Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2011-04-08 21:38 +0300
    Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-09 09:53 +1000
  Re: linux raid vs hw raid KR <kristian.rasmussen@broadpark.no.spam.com> - 2011-04-09 11:56 +0200
    Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-09 10:32 -0700
      Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-10 11:12 +1000
        Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-09 18:59 -0700
          Re: linux raid vs hw raid KR <kristian.rasmussen@broadpark.no.spam.com> - 2011-04-10 04:32 +0200
            Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-10 12:46 +1000
              Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-09 20:39 -0700
    Re: linux raid vs hw raid Robert Riches <spamtrap42@jacob21819.net> - 2011-04-10 03:47 +0000
      Re: linux raid vs hw raid Balwinder S Dheeman <bsd.SANSPAM@anu.homelinux.net> - 2011-04-10 11:11 +0530
        Re: linux raid vs hw raid Keith Keller <kkeller-usenet@wombat.san-francisco.ca.us> - 2011-04-09 23:29 -0700
          Re: linux raid vs hw raid Balwinder S Dheeman <bsd.SANSPAM@anu.homelinux.net> - 2011-04-10 14:05 +0530
        Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-10 20:16 +1000
          Re: linux raid vs hw raid Tim Watts <tw@dionic.net> - 2011-04-10 11:28 +0100
          Re: linux raid vs hw raid Balwinder S Dheeman <bsd.SANSPAM@anu.homelinux.net> - 2011-04-10 19:43 +0530
        Re: linux raid vs hw raid Robert Riches <spamtrap42@jacob21819.net> - 2011-04-12 03:44 +0000
          Re: linux raid vs hw raid Balwinder S Dheeman <bsd.SANSPAM@anu.homelinux.net> - 2011-04-12 13:56 +0530
      Re: linux raid vs hw raid Grant <omg@grrr.id.au> - 2011-04-10 20:09 +1000
        Re: linux raid vs hw raid Robert Riches <spamtrap42@jacob21819.net> - 2011-04-12 03:37 +0000

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