From: Anton Rommerskirchen
Subject: Re: SSD + RAID
Date: ,
Msg-id: 200911191901.14300.atr@atrsoft.de
(view: Whole thread, Raw)
In response to: Re: SSD + RAID  (Craig Ringer)
Responses: Re: SSD + RAID  (Brad Nicholson)
List: pgsql-performance

Tree view

SSD + RAID  (Laszlo Nagy, )
 Re: SSD + RAID  (Karl Denninger, )
  Re: SSD + RAID  (Laszlo Nagy, )
   Re: SSD + RAID  (Axel Rau, )
    Re: SSD + RAID  (Richard Neill, )
     Re: SSD + RAID  (Greg Smith, )
      Re: SSD + RAID  (Merlin Moncure, )
  Re: SSD + RAID  (Marcos Ortiz Valmaseda, )
 Re: SSD + RAID  (Scott Marlowe, )
  Re: SSD + RAID  (Merlin Moncure, )
   Re: SSD + RAID  (Scott Carey, )
    Re: SSD + RAID  (Merlin Moncure, )
 Re: SSD + RAID  (Heikki Linnakangas, )
  Re: SSD + RAID  (Merlin Moncure, )
   Re: SSD + RAID  (Heikki Linnakangas, )
    Re: SSD + RAID  (Merlin Moncure, )
     Re: SSD + RAID  (Heikki Linnakangas, )
      Re: SSD + RAID  (Merlin Moncure, )
  Re: SSD + RAID  (Laszlo Nagy, )
   Re: SSD + RAID  (Robert Haas, )
    Re: SSD + RAID  (Laszlo Nagy, )
 Re: SSD + RAID  (Greg Smith, )
  Re: SSD + RAID  (Karl Denninger, )
   Re: SSD + RAID  (Greg Smith, )
    Re: SSD + RAID  (Karl Denninger, )
     Re: SSD + RAID  (Scott Carey, )
      Re: SSD + RAID  (Tom Lane, )
       Re: SSD + RAID  (Jeff Janes, )
      Re: SSD + RAID  (Greg Smith, )
       Re: SSD + RAID  (Karl Denninger, )
    Re: SSD + RAID  (Brad Nicholson, )
     Re: SSD + RAID  (Dave Crooke, )
     Re: SSD + RAID  (Greg Smith, )
      Re: SSD + RAID  (Merlin Moncure, )
      Re: SSD + RAID  (Merlin Moncure, )
       Re: SSD + RAID  (Brad Nicholson, )
        Re: SSD + RAID  (Scott Marlowe, )
       Re: SSD + RAID  (Peter Eisentraut, )
       Re: SSD + RAID  (Greg Smith, )
        Re: SSD + RAID  (Merlin Moncure, )
         Re: SSD + RAID  (Greg Smith, )
          Re: SSD + RAID  (, )
           Re: SSD + RAID  (Scott Carey, )
            Re: SSD + RAID  (Merlin Moncure, )
             Re: SSD + RAID  (Scott Marlowe, )
              Re: SSD + RAID  (Greg Smith, )
               Re: SSD + RAID  (Merlin Moncure, )
                Re: SSD + RAID  (Scott Marlowe, )
        Re: SSD + RAID  (Mark Mielke, )
        Re: SSD + RAID  (Scott Carey, )
         Re: SSD + RAID  (Greg Smith, )
        Re: SSD + RAID  (Bruce Momjian, )
         Re: SSD + RAID  (Ron Mayer, )
          Re: SSD + RAID  (Bruce Momjian, )
           Re: SSD + RAID  (Greg Smith, )
            Re: SSD + RAID  (Bruce Momjian, )
             Re: SSD + RAID  (Ron Mayer, )
              Re: SSD + RAID  (Bruce Momjian, )
           Re: SSD + RAID  (Ron Mayer, )
  Re: SSD + RAID  (Merlin Moncure, )
  Re: SSD + RAID  (Matthew Wakeling, )
   Re: SSD + RAID  (Bruce Momjian, )
    Re: SSD + RAID  (Dan Langille, )
     Re: SSD + RAID  (Bruce Momjian, )
      Re: SSD + RAID  (Scott Carey, )
       Re: SSD + RAID  (Bruce Momjian, )
        Re: SSD + RAID  (Ron Mayer, )
         Re: SSD + RAID  (Greg Smith, )
          Re: SSD + RAID  (Arjen van der Meijden, )
           Re: SSD + RAID  (Greg Smith, )
            Re: SSD + RAID  (Mark Mielke, )
             Re: SSD + RAID  (Greg Smith, )
              Re: SSD + RAID  (Scott Marlowe, )
               Re: SSD + RAID  (Scott Marlowe, )
                Re: SSD + RAID  ("Pierre C", )
                 Re: SSD + RAID  (Nikolas Everett, )
                 Re: SSD + RAID  (Scott Carey, )
          Re: SSD + RAID  (Bruce Momjian, )
           Re: SSD + RAID  (Ron Mayer, )
            Re: SSD + RAID  (Greg Smith, )
            Re: SSD + RAID  (, )
             Re: SSD + RAID  (, )
              Re: SSD + RAID  (Aidan Van Dyk, )
               Re: SSD + RAID  (, )
                Re: SSD + RAID  (Mark Mielke, )
                Re: SSD + RAID  (Dave Crooke, )
          Re: SSD + RAID  (Bruce Momjian, )
           Re: SSD + RAID  (Greg Smith, )
            Re: SSD + RAID  (Bruce Momjian, )
             Re: SSD + RAID  (Ron Mayer, )
              Re: SSD + RAID  (Greg Smith, )
               Re: SSD + RAID  (Bruce Momjian, )
              Re: SSD + RAID  (Bruce Momjian, )
               Re: SSD + RAID  (Greg Smith, )
                Re: SSD + RAID  (Ron Mayer, )
               Re: SSD + RAID  ("Pierre C", )
         Re: SSD + RAID  (Bruce Momjian, )
 Re: SSD + RAID  ("Fernando Hevia", )
  Re: SSD + RAID  (Greg Smith, )
 Re: SSD + RAID  ("Kenny Gorman", )
  Re: SSD + RAID  (Kenny Gorman, )
 Re: SSD + RAID  (Lists, )
  Re: SSD + RAID  (Ivan Voras, )
   Re: SSD + RAID  (Laszlo Nagy, )
    Re: SSD + RAID  (Craig Ringer, )
     Re: SSD + RAID  (Laszlo Nagy, )
      Re: SSD + RAID  (Craig Ringer, )
       Re: SSD + RAID  (Laszlo Nagy, )
     Re: SSD + RAID  (Craig James, )
      Re: SSD + RAID  (Heikki Linnakangas, )
     Re: SSD + RAID  (Scott Carey, )
      Re: SSD + RAID  (Craig Ringer, )
       Re: SSD + RAID  (Anton Rommerskirchen, )
        Re: SSD + RAID  (Brad Nicholson, )
      Re: SSD + RAID  (Greg Smith, )
       Re: SSD + RAID  (Matthew Wakeling, )
       Re: SSD + RAID  (Scott Carey, )

Am Donnerstag, 19. November 2009 13:29:56 schrieb Craig Ringer:
> On 19/11/2009 12:22 PM, Scott Carey wrote:
> > 3:  Have PG wait a half second (configurable) after the checkpoint
> > fsync() completes before deleting/ overwriting any WAL segments.  This
> > would be a trivial "feature" to add to a postgres release, I think.
>
> How does that help? It doesn't provide any guarantee that the data has
> hit main storage - it could lurk in SDD cache for hours.
>
> > 4: Yet another solution:  The drives DO adhere to write barriers
> > properly. A filesystem that used these in the process of fsync() would be
> > fine too. So XFS without LVM or MD (or the newer versions of those that
> > don't ignore barriers) would work too.
>
> *if* the WAL is also on the SSD.
>
> If the WAL is on a separate drive, the write barriers do you no good,
> because they won't ensure that the data hits the main drive storage
> before the WAL recycling hits the WAL disk storage. The two drives
> operate independently and the write barriers don't interact.
>
> You'd need some kind of inter-drive write barrier.
>
> --
> Craig Ringer


Hello !

as i understand this:
ssd performace is great, but caching is the problem.

questions:

1. what about conventional disks with 32/64 mb cache ? how do they handle the
plug test if their caches are on ?

2. what about using seperated power supply for the disks ? it it possible to
write back the cache after switching the sata to another machine controller ?

3. what about making a statement about a lacking enterprise feature (aka
emergency battery equipped ssd) and submitting this to the producers ?

I found that one of them (OCZ) seems to handle suggestions of customers (see
write speed discussins on vertex fro example)

and another (intel) seems to handle serious problems with his disks in
rewriting and sometimes redesigning his products - if you tell them and
market dictades to react (see degeneration of performace before 1.11
firmware).

perhaps its time to act and not only to complain about the fact.

(btw: found funny bonnie++ for my intel 160 gb postville and my samsung pb22
after using the sam for now approx. 3 months+ ... my conclusion: NOT all SSD
are equal ...)

best regards

anton

--

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