Am Donnerstag, 10. Mai 2007 schrieb Feizhou:
> Andreas Micklei wrote:
> > Am Mittwoch, 9. Mai 2007 schrieb Feizhou:
> >>> HW vs SW RAID: Kind of a religious question. HW has some advantages
> >>> when using RAID-5 or RAID-6 (less CPU load). When using RAID-0 or
> >>> RAID-1 there should not be any difference performance wise. HW RAID
> >>> gives you some advantages in terms of handling, i.e. hotplugging of
> >>> discs, nice administration console, RAID-10 during install ;-), etc.
> >>> It's up to you to decide whether it is worth the money. Plus you need
> >>> to find a controller that is well supported in Linux.
> >>
> >> Hardware raid that comes with bbu write caches normally have a speed
> >> boost in addition to the extra data safety too.
> >
> > Also on RAID-0 and RAID-1? I have only used HW RAID without bbu, so I
> > have no experience with that. However you can tweak your filesystem and
> > disks to do write caching too, especially if you have plenty of RAM. Of
> > course this means living dangerously, so when you need performance and
> > data safety HW RAID with bbu is the only option of course.
>
> Why did you think I specifically said hardware raid that comes with bbu
> memory caches?
Because you said "Hardware raid that comes with bbu write caches normally have
a speed boost in addition to the extra data safety too."? ;-)
> RAM will always be faster than disk so if the hardware
> raid stores stuff first in a bbu memory cache, it will always beat
> software raid even on raid0,raid1.
Does'nt Linux have a memory cache on it's own? Putting lot's of RAM into a
machine, using a fast filesystem, i.e. XFS and tuning it to not write
everything to disc immideately should give equal performance. It should be
even better, because you can put much more RAM into a machine than on the
RAID controller.
Of course this does not give you the same level of data safety. Far from it!
> Hardware raid without a bbu memory cache will always be slower on raid5
> even if the raid processor is beefy enough.
I use HW RAID with a memory cache but without bbu which gives the same level
of performance. Of course this is dangerous and might eat the data when the
machine dies. However with redundant power supply and UPS this is not so
likely (and yes, we have backups).
--
Andreas Micklei
IVISTAR Kommunikationssysteme AG
Ehrenbergstr. 19 / 10245 Berlin, Germany
http://www.ivistar.de
Handelsregister: Berlin Charlottenburg HRB 75173
Umsatzsteuer-ID: DE207795030
Vorstand: Dr.-Ing. Dirk Elias
Aufsichtsratsvorsitz: Dipl.-Betriebsw. Frank Bindel
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