RAID & Swap.

["Aaron D. Turner" <aturner@best.com>]

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Below is an excellent email I recieved regarding RAID and swap partitions.
The decision we need to make is 256MB of RAM good enough for now, or do we
want to put the swap partitions on unmirrored partitions (single point of
failure).

IMHO, we're better off not running any swap partitions and just hitting up
VA for more RAM if/when we need it.  Maybe I'm being paranoid (after all
what's the real chance that one of those disks will fail??? not likely),
but that's the way I am with H/A.   Murfy's Law and all that.


- -- 
Aaron Turner           | Either which way, one half dozen or another. 
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- ---------- Forwarded message ----------
From: m. allan noah <anoah@pfeiffer.edu>
To: Aaron Turner <aturner@pobox.com>
Date: Mon, 4 Jan 1999 18:44:13 -0500 (EST)
Subject: Re: RAID1 on / for RH 5.2

no. never swap to raid > 0. never.

raid driver allocates ram dynamically to write to multiple drives at once.
(basically, you write to the fs, which writes to the vfat, which writes to
the md driver, which allocates ram to hold that block while it sends the
data across to multiple disks.)

you are swapping to this cause you need ram. attempting to allocate ram to
do this, requires more swapping, which requires more swapping. oh shit,
swap full in under a second. system crash.

raid level 0 can give a performance boost to swap. but, it will still be
1000x slower than ram. swap performance should never be an issue, buy more
ram. if swap security is your issue (i would expect it is...) too bad, you
need a hardware solution to swap to. of course, by the time you buy a
hardware controller, and its performance is worse than the software raid
driver, you should have bought more ram.

in short, software raid and swap dont mix. more ram and raid do. go to 512
meg.

al

Paranoid: So who's in charge of thinking up cool stuff to put in 2.3?
      AC: You are. Thats why its called Open Source.




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