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From:Dan Nelson Date:August 22 2003 2:50am
Subject:Re: RAID or not?
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In the last episode (Aug 21), Jon Drukman said:
> Lefevre, Steven wrote:
> >I say go with RAID 5, on a controller card.
> > Mirroring just gives you backup, and you lose half your diskspace.
> > It offers no performance benefit, and actually the computer might
> > have to work harder to make sure the drives are in sync.
> 
> that is not true.  mirroring gives you double the read speed and half
> the write speed.  RAID5 gives you less than half the write speed.

Software raid5 gives you around 1/4 the write speed, to be exact. 
Hardware raid5 with battery-backed cache can completely remove the
penalty, by either waiting for an entire stripe of data to flush in one
operation, or delaying the extra I/O operations until the disk head
happens to be near that block anyway (or until the disk is otherwise
idle).  Make sure you max out the RAM in your raid card; it's cheap.

-- 
	Dan Nelson
	dnelson@stripped
Thread
RAID or not?Jackson Miller21 Aug
  • Re: RAID or not?Jon Drukman21 Aug
    • Re: RAID or not?Jackson Miller21 Aug
      • RE: RAID or not?Steven) (Lefevre21 Aug
        • Re: RAID or not?David Griffiths21 Aug
        • Re: RAID or not?Per Andreas Buer21 Aug
        • Re: RAID or not?Jon Drukman22 Aug
          • Re: RAID or not?Dan Nelson22 Aug
          • RE: RAID or not?Steven) (Lefevre22 Aug
            • RE: RAID or not?Michael Loftis2 Sep
  • Re: RAID or not?Colbey21 Aug
  • Re: RAID or not?Per Andreas Buer21 Aug
RE: RAID or not?Alec.Cawley22 Aug
  • Re: RAID or not?Jim McAtee23 Aug
    • Re: RAID or not?Michael Loftis2 Sep
RE: RAID or not?Alec.Cawley22 Aug
Re: RAID or not?Alec.Cawley26 Aug