[OpenIndiana-discuss] Swap during install

Rob McMahon RobMcMahonCV at gmail.com
Tue Sep 25 13:37:49 UTC 2012

On 25/09/2012 13:50, Richard Elling wrote:
> Use what you need. Most people don't need or want to use swap. Why? Because...
> if you have to swap, performance will suck. Period. Case closed. Game, set, match.
> HDDs are 5 orders of magnitude slower than RAM and all the king's horses and all
> the king's men can't fix that.
> The old rule of "2x" RAM has not been true since around the time you could put 1GB of
> RAM into a machine. Interestingly, the place we normally see vehement arguments for
> 2x RAM is from Oracle DBAs who believe everything ever written in an Oracle manual :-)
> hint: run "swap -l" and see if free == blocks. If so, then you've never used
> swap since the system was booted.
Hmm, I was under the impression that you needed swap available (even if 
never used) for a big program that forked and then exec'ed, just in case 
that memory was written.  In other words that
1) Solaris played it safe, and would not allow a fork if insufficient 
swap (including memory) was available, even if it was never used, whereas
2) Linux would blindly let it continue with the possibility of killing 
some other process in the case that the memory *was* needed.
Not true ?

 > swap -l
No swap devices configured
 > swap -s
total: 1336200k bytes allocated + 294428k reserved = 1630628k used, 
1901028k available
 > swap -a /dev/zvol/dsk/rpool/swap
 > swap -s
total: 1347884k bytes allocated + 314552k reserved = 1662436k used, 
6056804k available
 > swap -l
swapfile             dev    swaplo   blocks     free
/dev/zvol/dsk/rpool/swap 182,1         8  8388600  8383624


E-Mail:	Rob.McMahon at warwick.ac.uk		PHONE:  +44 24 7652 3037
Rob McMahon, IT Services, Warwick University, Coventry, CV4 7AL, England

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