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Re: Problems adding swap files

On 15 May 1997, Rob Browning wrote:

> Pete Templin <templin@bucknell.edu> writes:
> > As my system is currently laid out, I'm not suffering from any shortage of
> > swap _space_ (240MB allocated, max seen in use is 33MB), I'm merely trying
> > to sneak out the best possible performance without spending a buck.
> In the end I imagine you'll be much happier if you scrounge for more
> RAM, but you probably already knew that...

Yeah.  I sold one of my systems a few weeks ago (it was recommissioned to
become the official "lists.debian.org", but that idea got nixed by
organizational politics and miscommunications...and I needed some cash :)
While it was waiting to be sold, I treated myself to 64, and I really miss
> > I think I'm just having trouble using a swapfile on a md array, as opposed
> > to a pathname problem.  Any ideas would, of course, be gladly accepted.
> I'm not sure I understand your problem, but I'll be happy to help if I
> can.  We have machines here using /dev/md0 as swap.  Is that roughly
> what you are trying to accomplish?

Actually, I've got an ext2 filesystem on my /dev/md0 that is 6GB, and I
had wanted to sneak a few swapfiles into that filesystem.  Between errors
getting this going and Mike Neuffer's email a moment ago:

Mike Neuffer writes:
> You don't wan't to have your swap partitions on an MD device.
> The kernel already stripes over all available swap partitions.
> Using MD just wastes CPU cycles.

I think I'll just leave things go or hunt for other partition
rearrangements that have better performance.
> Here's the mdtab.
> # mdtab entry for /dev/md0
> /dev/md0  raid0,4k,0  /dev/hda2 /dev/hdb2
> # mdtab entry for /dev/md1
> /dev/md1  raid0,4k,0  /dev/hda3 /dev/hdb3
> # mdtab entry for /dev/md2
> /dev/md2  raid0,4k,0  /dev/hda4 /dev/hdb4

What kind of performance do you get with your md devices?  It seems to me
(operating in a vacuum not knowing what other disks you have) that you'd
do better by shifting your hdb (primary slave IDE disk) to hdc (secondary
master IDE) if you've got it available.  IDE can only control either
master or slave on a given controller at a time, so your md arrays are
probably being accessed very choppily.  Keep in mind that moving a disk
can spell temporary disaster, as you'll have to rebuild your /etc/fstab
and your /etc/mdtab appropriately.  Also, some BIOSes won't allow booting
from hdc (which means that LILO won't work either), so don't move it if
your / is on that drive.


Peter J. Templin, Jr.                   Client Services Analyst
Computer & Communication Services       tel: (717) 524-1590
Bucknell University			templin@bucknell.edu

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