Re: Is Read speed faster when 1 disk is failed on raid5 ?

[Jakob Oestergaard <jakob@unthought.net>]

On Tue, Oct 22, 2002 at 11:58:56AM +0200, raid@ddx.a2000.nu wrote:
> On Tue, 22 Oct 2002, Chris Siebenmann wrote:
> >  At a guess: when RAID-5 is intact, the kernel must read the entire
> > stripe size worth of data to verify the parity. When a RAID-5 array has
> > a dead disk, any intact data block can be handed to the application
> > the moment it comes off the disk as there is no point in doing parity
> > verification. (The kernel has to reconstruct the missing blocks, but
> > most of the blocks are present and good.)
> 
> i thought raid5 was doing parity calculation when writing ?

Correct. RAID-5 will not do parity calculation when reading. RAID-5 will
give you availability but it will not give you integrity.

> difference between rading from failed an intact raid5 is almost twice the
> speed (failed is doing 150MB/sec, intact is doing 80MB/sec)

I didn't follow the beginning of this thread, sorry.  Is this SCSI?

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:
-
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html