Re: Hardware vs Software RAID

От: Peter T. Breuer
Тема: Re: Hardware vs Software RAID
Дата: ,
Msg-id: 200806251311.m5PDBNv23559@inv.it.uc3m.es
(см: обсуждение, исходный текст)
Ответ на: Re: Hardware vs Software RAID  (Matthew Wakeling)
Ответы: Re: Hardware vs Software RAID  (Greg Smith)
Список: pgsql-performance

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Hardware vs Software RAID  (Adrian Moisey, )
 Re: Hardware vs Software RAID  ("Merlin Moncure", )
  Re: Hardware vs Software RAID  (Matthew Wakeling, )
   Re: Hardware vs Software RAID  ("Peter T. Breuer", )
    Re: Hardware vs Software RAID  (Greg Smith, )
     Re: Hardware vs Software RAID  ("Jonah H. Harris", )
      Re: Hardware vs Software RAID  ("Joshua D. Drake", )
     Re: Hardware vs Software RAID  (Matthew Wakeling, )
      Re: Hardware vs Software RAID  (Vivek Khera, )
       Re: Hardware vs Software RAID  (Matthew Wakeling, )
        Re: Hardware vs Software RAID  ("Scott Marlowe", )
        Re: Hardware vs Software RAID  ("Merlin Moncure", )
         Re: Hardware vs Software RAID  (Matthew Wakeling, )
          Re: Hardware vs Software RAID  ("Merlin Moncure", )
     Re: Hardware vs Software RAID  ("Peter T. Breuer", )
      Re: Hardware vs Software RAID  (Greg Smith, )
     Re: Hardware vs Software RAID  (Robert Treat, )
   Re: Hardware vs Software RAID  ("Merlin Moncure", )
    Re: Hardware vs Software RAID  ("Peter T. Breuer", )
     Re: Hardware vs Software RAID  ("Merlin Moncure", )
      Re: Hardware vs Software Raid  ("Peter T. Breuer", )
       Re: Hardware vs Software Raid  ("Merlin Moncure", )
       Re: Hardware vs Software Raid  (, )
       Re: Hardware vs Software Raid  (Greg Smith, )
 Re: Hardware vs Software RAID  ("Scott Marlowe", )
  Re: Hardware vs Software RAID  ("Joshua D. Drake", )
   Re: Hardware vs Software RAID  ("Merlin Moncure", )
    Re: Hardware vs Software RAID  (Andrew Sullivan, )
     Re: Hardware vs Software RAID  ("Kevin Grittner", )
      Re: Hardware vs Software RAID  (Andrew Sullivan, )
     Re: Hardware vs Software RAID  (Greg Smith, )
    Re: Hardware vs Software RAID  (Greg Smith, )

"Also sprach Matthew Wakeling:"
> >> Has anyone done some benchmarks between hardware RAID vs Linux MD software
> >> RAID?
  ...
> > The upshot is I don't really see a difference in performance.
>
> The main difference is that you can get hardware RAID with
> battery-backed-up cache, which means small writes will be much quicker
> than software RAID. Postgres does a lot of small writes under some use

It doesn't "mean" that, I'm afraid.  You can put the log/bitmap wherever
you want in software raid, including on a battery-backed local ram disk
if you feel so inclined.  So there is no intrinsic advantage to be
gained there at all.

> However, not all hardware RAID will have such a battery-backed-up cache,
> and those that do tend to have a hefty price tag.

Whereas software raid and a firewire-attached log device does not.


Peter


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