Re: Two hard drives --- what to do with them?

От: Bruno Wolff III
Тема: Re: Two hard drives --- what to do with them?
Дата: ,
Msg-id: 20070301032846.GA14102@wolff.to
(см: обсуждение, исходный текст)
Ответ на: Re: Two hard drives --- what to do with them?  ("Peter Kovacs")
Список: pgsql-performance

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 Re: which Xeon processors don't have the context switching problem  ("Claus Guttesen", )
 Re: which Xeon processors don't have the context switching problem  ("Steinar H. Gunderson", )
  Re: which Xeon processors don't have the context switching problem  (Alvaro Herrera, )
   Re: which Xeon processors don't have the context switching problem  ("Steinar H. Gunderson", )
   Re: which Xeon processors don't have the context switching problem  (Magnus Hagander, )
 Re: which Xeon processors don't have the context switching problem  (Josh Berkus, )
  Re: which Xeon processors don't have the context switching problem  (Geoffrey, )
  Re: which Xeon processors don't have the context switching problem  ("Joshua D. Drake", )
   Re: which Xeon processors don't have the context switching problem  (Geoffrey, )
    Re: which Xeon processors don't have the context switching problem  ("Guillaume Smet", )
     Re: which Xeon processors don't have the context switching problem  (Geoffrey, )
      Re: which Xeon processors don't have the context switching problem  ("Joshua D. Drake", )
       Two hard drives --- what to do with them?  (Carlos Moreno, )
        Re: Two hard drives --- what to do with them?  (Tom Lane, )
         Re: Two hard drives --- what to do with them?  ("Peter Kovacs", )
          Re: Two hard drives --- what to do with them?  (Jeff Davis, )
           Re: Two hard drives --- what to do with them?  ("Peter Kovacs", )
            Re: Two hard drives --- what to do with them?  (Jeff Davis, )
             Re: Two hard drives --- what to do with them?  (Shane Ambler, )
              Re: Two hard drives --- what to do with them?  ("Peter Kovacs", )
               Re: Two hard drives --- what to do with them?  (Ben, )
               Re: Two hard drives --- what to do with them?  (Shane Ambler, )
                Re: Two hard drives --- what to do with them?  (Bruno Wolff III, )
               Re: Two hard drives --- what to do with them?  (Jeff Davis, )
                Re: Two hard drives --- what to do with them?  (Scott Marlowe, )
              Re: Two hard drives --- what to do with them?  (Bruno Wolff III, )
          Re: Two hard drives --- what to do with them?  (Bruno Wolff III, )
        Re: Two hard drives --- what to do with them?  (Alexander Staubo, )
       Re: which Xeon processors don't have the context switching problem  (Geoffrey, )
   Re: which Xeon processors don't have the context switching problem  ("Guillaume Smet", )

On Sun, Feb 25, 2007 at 23:11:01 +0100,
  Peter Kovacs <> wrote:
> A related question:
> Is it sufficient to disable write cache only on the disk where pg_xlog
> is located? Or should write cache be disabled on both disks?

With recent linux kernels you may also have the option to use write
barriers instead of disabling caching. You need to make sure all of
your stacked block devices will handle it and most versions of software
raid (other than 1) won't. This won't be a lot faster, since at sync
points the OS needs to order a cache flush, but it does give the disks a chance
to reorder some commands in between flushes.


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