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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