Re: Hardware vs Software RAID

От: Matthew Wakeling
Тема: Re: Hardware vs Software RAID
Дата: ,
Msg-id: Pine.LNX.4.64.0806251355090.4085@aragorn.flymine.org
(см: обсуждение, исходный текст)
Ответ на: Re: Hardware vs Software RAID  ("Merlin Moncure")
Ответы: Re: Hardware vs Software RAID  ("Peter T. Breuer")
Re: Hardware vs Software RAID  ("Merlin Moncure")
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, )

On Wed, 25 Jun 2008, Merlin Moncure wrote:
>> Has anyone done some benchmarks between hardware RAID vs Linux MD software
>> RAID?
>
> I have here:
> http://merlinmoncure.blogspot.com/2007/08/following-are-results-of-our-testing-of.html
>
> 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
cases.

Without a BBU cache, it is sensible to put the transaction logs on a
separate disc system to the main database, to make the transaction log
writes fast (due to no seeking on those discs). However, with a BBU cache,
that advantage is irrelevant, as the cache will absorb the writes.

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

Matthew

--
$ rm core
Segmentation Fault (core dumped)


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