From: Jakma, Paul (Paul.Jakma at domain compaq.com)
Date: Thu 03 Feb 2000 - 13:08:29 GMT
> The implication being that resize2fs doesn't handle 4kb blocksizes
> correctly. Eeeek. Scary! :-)
don't worry. resize2fs just refuses to resize 4kb fs's. It doesn't mangle
> Sorry, hadn't considered the possibility that somebody might do raid5
> without writeback enabled. *Shudder*
well.. writeback is very dangerous. Especially with any kind of journalling
fs, in which case you should not use writeback without proper protection, eg
your controller should have a battery backup module.
> Even with writeback, any raid5 implementation I've used (*)
> has sucked. You
then the controller is parity-bound. RAID5 should be faster at writing than
RAID1 if the controller can do the parity calculations fast enough.
> fill up the the writeback cache and everything goes dog slow.
> Even with,
> say, 128MB of bb writeback cache, you can fill it up too easily, and
> it empties at a handful of megabytes a second. :-(
> (*) Of course, I've only ever used sucky raid5 implementations. :-)
> DPT and Megaraid, and a couple of yellow pack dedicated external
> arrays. What are the others, like Mylex and ICP like? How about
> dedicated external boxes like compaq's storageworkses...?
Mylex is pretty decent iirc. At least 10MB/s block output from bonnie i
think (4mb cache writeback, old DAC960-PDU). I'll try find a box to run some
Best way to judge them imo is to look at the CPU, as it will determine the
RAID5 performance. The older DAC960's were i960 based, and even the slowest
of them, i960CF at domain 25MHz on the DAC960-PDU that i used was still reasonably
fast. Newer DAC960 use i960 at domain 33 and 66MHz and the ExtremeRAID's use
StrongARM chips which should be very fast.
The older Compaq SMARTarray-2's were AMD 29K based. Never benchmarked them,
but they seemed decent. I've no idea what the new range of Compaq
controllers use - never seen them. I assume they're faster than the older
I've never used external arrays, so can't comment. But i guess they're very
> As for the disk space issue, disks are cheap. Raid5 is great
> where you
disks are cheap.. true. But i'd rather have 27GB of disk space with RAID5
than 18GB with RAID1. And RAID5 is much faster for reads, and should be
decent for writes if the controller is up to it. Why waste 16% drive space,
(25% with 4 drives!!). Rack space isn't cheap either.
And if money isn't a problem, then why not spend it on a beefier controller?
Then you can have everything...
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