Ivan Voras wrote: > On 07/11/2007, Arne Wörner <arne_woerner_at_yahoo.com> wrote: > >> graid5 puts write requests for about kern.geom.raid5.wdt seconds (but not less >> than 1-2 seconds) into the write cache (if there is enough space left in >> graid5's write cache)... I would guess that this behaviour is pretty >> incompatible with soft-updates with power outage... > > Can this cache be disabled? Probably - but recent info shows it to be the prime mover in providing decent performance (when things are NOT broken). > >> Then there still is the write cache of the hard discs (I dont know how long it >> waits, but that time would come in addition to graid5's delay)... >> >> Maybe gjournal could help, because graid5 honors the BIO_FLUSH, but that is >> untested... > > Yes, AFAIK this would work. > A RAID5 is one of the harder ones to do both fast and well in software-only. The better hardware ($$$) controllers have fast hardware XOR engines as well as CPU-as-state-machines and battery-backed cache, and THEY have to work hard. Further, a hardware controller sits in the right place to do the job well, the 'GP' CPU(s) - no matter they have spare cycles to burn - do not. I don't think even GEOM magic can get around that w/o user willingness to take on some unavoidable compromises. Given decent hardware & any UPS that costs less than the hardware controller, these are 'choices' - not really show-stoppers. BillReceived on Wed Nov 07 2007 - 12:09:02 UTC
This archive was generated by hypermail 2.4.0 : Wed May 19 2021 - 11:39:21 UTC