[svlug] Performance and memory
Karsten M. Self
kmself at ix.netcom.com
Sat Apr 30 00:39:39 PDT 2005
on Fri, Apr 29, 2005 at 11:45:06PM -0700, Jeffrey Siegal (jbs at quiotix.com) wrote:
> On Apr 29, 2005, at 18:34, Karsten M. Self wrote:
> >> Another issue with swap is the speed, type, and layout of your
> >> harddrives. If your swapping to the same IDE drive it's trying to
> >> read
> >> the incoming program/data from, you'll bottleneck as IDE only does 1
> >> transaction per controller per interval.
> > Yep. RAID will buy you _massive_ benefits here (the controller handles
> > the i/o, the CPU doesn't block), for good values of RAID controller.
> > Dittos SCSI.
> Yes and no. A better storage subsystem will improve your swapping
> performance, but that's rearranging the proverbial deck chairs. In
> reality you are *far* better off in almost all cases just getting
> enough memory that you aren't swapping so much.
> Faster disk subsystems (RAID, SCSI, etc.) are a good solution when you
> need persistent storage (mostly databases). If you need more memory,
> get more memory.
But the impact of disk, particularly slow or contended disk, is pretty
Two case studies:
1. A consultancy I worked for in the mid 1990s had, by 2003, the same
HP 9000K<mumble> midrange HPUX server bought new in 1997. And some
other Unix kit. And a bunch of x86 legacy MS Windows systems.
Heavy lifting app was SAS. x86 ran circles around the RISC kit for
CPU intensive stuff.
But for raw I/O, it was the 6 year old HP that had the best
performance. Nothing beats fast disk, good channels, and IIRC, a
sane RAID setup.
2. About the same time, I was running SAS, also on legacy MS Windows,
on a then-current Dell box, 2.4 GHz, 384 MiB or so, 7200 RPM ATA
disk. A fire-sale 3u server was aquired, and for shits'n'grins, SAS
loaded. 500 MHz, 1 GiB RAM, dual SCSI disks, striped for the
Straight read/write ops were 2x faster than the "faster" Dell.
A more complex analysis routine involving multiple subqueries and
table creations and reads, was 10x faster on the SCSI striped
My own system here (based on laptop 4200 RPM disk, tuned w/ hdparm to
a blazing <coff> 6.13 MiB/s, gets really heavily contended in some
processing and cron.daily tasks. I watch system load climg at these
times. 1 GiB RAM really doesn't do much, nor does a 1.7 GHz processor,
not when a single-spindle, one-task-at-a-time disk gets in the way.
The real key is: Know your system and its bottlenecks. Apply remedies
Karsten M. Self <kmself at ix.netcom.com> http://kmself.home.netcom.com/
What Part of "Gestalt" don't you understand?
Free Software Primer -- concepts you need to understand
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