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Re: [K12OSN] need some K12LTSP 5.0EL advice



On Wed, 2007-07-25 at 09:39 -0700, Robert Arkiletian wrote:
> On 7/25/07, James P. Kinney III <jkinney localnetsolutions com> wrote:
> > You will ALWAYS need a swap partition for the OS. The standard 2GB swap
> > partition is OK. If you are using software RAID1, create the a pair of
> > 1GB swap partitions and let swap handle them outside of RAID. Putting
> > swap on a mirror is a waste of system resources. If you are using
> > hardware RAID you will have no choice but to put swap on the mirror or
> > add a third drive.
> 
> Not sure if I agree. Using 2 or more disks with swap partitions causes
> linux to effectively use those partitions with striping (RAID 0), thus
> 1GB+1GB=2GB with no redundancy. The point of having RAID 1 is so your
> system doesn't go down if one disk fails. Suppose you exhaust RAM and
> go into swap and that disk fails. You have just lost virtual RAM.
> Crash. That's why I also put my swap on RAID 1.

I agree that that process makes a "fake raid1". But it's swap not data.
Yes it will crash if a drive fails. But if a drive fails, I've got
bigger problems that lost swap data (which just gets purges on the next
reboot anyway). Disk failure will not always cause a system crash. Also
by having split swap areas, the ability to turn off swap, deactivate a
swap partition and turn on swap is nice.

The big advantage is spreading the swap strip over more than one spindle
makes for a performance boost. At the point where swap is used, we are
into system bog-down mode. 

I have designed a 3 drive mirrored swap setup that just had HA written
all over it. It was designed specifically to not die during a drive
failure for any reason.

2 identically sized partitions per each of three drives 1a, 1b, 2a, 2b,
3a, 3b. RAID1 of 1a+2a, 1b+3a, 2b+3b. This makes 3 mirrored partition to
use for swap. The rest of the drive was also carved up into other RAID1
sections. Loose any drive and the system still works plus on drive
replacement the recovery is not as performance damaging as a single
drive as mirror master.
> -- 
> Robert Arkiletian
> Eric Hamber Secondary, Vancouver, Canada
> Fl_TeacherTool http://www3.telus.net/public/robark/Fl_TeacherTool/
> C++ GUI tutorial http://www3.telus.net/public/robark/
> 
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> 
-- 
James P. Kinney III          
CEO & Director of Engineering 
Local Net Solutions,LLC        
770-493-8244                    
http://www.localnetsolutions.com

GPG ID: 829C6CA7 James P. Kinney III (M.S. Physics)
<jkinney localnetsolutions com>
Fingerprint = 3C9E 6366 54FC A3FE BA4D 0659 6190 ADC3 829C 6CA7

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