Can anyone confirm high CPU utilization on a 500+GB Software RAID 5 using
Promise controllers, Kernel 2.4.2 and UDMA 100 drives? All I have running
this thing is a PII-300 with 768MB RAM so I'll need to know if I'll need
more CPU cycles or if I'll be okay with what I've got.
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of Kanoa Withington
> Sent: April 17, 2001 2:22 PM
> To: Holger Kiehl
> Cc: Jason A. Lixfeld; [EMAIL PROTECTED]
> Subject: Re: Looking for the best solution
>
>
> A word of caution here, I do find CPU usage to be very high for 500+gb
> IDE software RAID5 arrays. At least for the 2.2.16 kernel, perhaps it's
> better under 2.4.x. I have a few 800+gb arrays with 2x800mhz PIII
> processors and CPU definetly appears to be the limiting resource. Same
> goes for 400+gb arrays with 2x700mhz processors.
>
> -Kanoa
>
> Holger Kiehl wrote:
>
> >
> > On Tue, 17 Apr 2001, Jason A. Lixfeld wrote:
> >
> >> Should I stay away from ReiserFS if I'm going to go with
> Software RAID 5?
> >> The fact that the filesystem doesn't need to be fscked is
> amazing, but it's
> >> taking 3 days to resize_reiserfs -s -60G from an LV right now
> so I assume
> >> resizing a reiserfs'd raid 5 will be the same? Also, I saw a
> benchmark with
> >> the 2 3Ware cards illustrating that RAID 5 with ReiserFS
> performed EXTREAMLY
> >> poorly compared against an the same ext2 RAID 5 configuration. Can you
> >> confirm/deny this? I'm going to be using 3-4 Promise Ultra100
> cards, not
> >> 3Ware, but I just want to know the benchmarks if anyone has any.
> >>
> > I also noticed this, ReiserFS with Software Raid 5 is extremly
> slow. I wonder
> > if there are any options to tune ReiserFS like the stride
> option in ext2?
> >
> >> How long does it take to resynch or rebuild if you add a drive/have a
> >> failure and need to rebuild to the hot spare?
> >>
> > This depends on how much activity you have and the size of the
> array, but you
> > can tune this very nicely in /proc/sys/dev/md/speed-limit
> (can´t remember the
> > location for 2.4.x). And here you can set it to a maximum of
> what your disk
> > can manage.
> >
> >> FINALLY (promise) I hear there are certain rather hefty
> CPU/RAM requirments
> >> for Software RAID 5. How do you generally need for a 500+GB
> Software RAID
> >> 5?
> >>
> > RAM requirements in my opinion is very low. I have a very busy
> 32 GB Software
> > Raid 5 here and cannot say that it is eating much of my CPU time. This
> > rumor that Software Raid eats lots of CPU time, in my opinion,
> is no longer
> > true.
> >
> > Holger
> >
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