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Re: [HELP] RAID chunk-size - alternatives

hi ya dave

ypppers on your comments...

another major point...

- raid protects aginst disk failure ...  but if raid wont
  come back online ... ( not mountable ) ... you lose all
  data ...
	-->> make sure your data is backed elsewhere
	and tested

On Tue, 2 Apr 2002, Dave Sherohman wrote:

> Since I'm feeling bored at the moment...
> On Tue, Apr 02, 2002 at 02:29:28PM -0800, Alvin Oga wrote:
> > typically a minimum of 2 disks used for raid0 or raid1...
> > 	raid1(mirroring) protects against one disk failure
> > 	( one disk's capacity is used as a redundant copy and not for user)
> > 		( 50% lost of space )
> Correction:  Protects against loss of all-but-one disks.  A 10-way
> mirror can drop 9 disks without losing any data.

fun stuff if one did that many mirrors...
	- i'd probably shoot um too if it was done in production
	environment .... :-)

> > 	raid0(stripping) does not help for disk failures
> A stripe set is more vulnerable to disk failure than a non-RAID
> solution.  If you're not using RAID, a failed drive only takes out
> the data on that one disk.  With RAID0, a failed drive will cost you
> most (if not all) of the data on the array.

yupp...  stripping doesNOT protect the raid against disk failures...
supposedly stripping is good if you wanna read data faster than normal..
> > typically 5 disks for raid5 ... 
> > 	( 3 disks mininum -- 1/3 of your disks lost to parity
> > 	( 4 disks .......... 1/4 of your disks lost to parity
> > 	( 5 disks .......... 1/5 of your disks lost to parity
> Don't know where you got the "typically 5 disks" bit from.  RAID5
> costs you one drive's worth of capacity.  Also, if I were to set up a
> 5-disk RAID5 for critical data, I'd go with 4 active disks, plus one
> spare.

hummm i've never gotten hotswap to work right...

	- always had to wait for resync time ( usually hours-n-hours )...
	and inevitably...shutdown anyway... to verify everything is clean
	resync and rebuild time is pretty heavy price tag on xxxGB raid

	during the rsync/rebuild time ... is when its probablygonna
	die some more if one keep writing more data to the degraded
	raid system ... since one has not found out why the original
	problem caused the raid to enter degraded mode

> > typically raid01 - needs 4 disks ...
> > 	first data is stripped across 2 disks than its mirrored to 2 more disks
> > 	- due to mirroring... 2 disks is lost for "mirror"
> Minimum 4 disks, but any larger even number of active disks will work.
> Here again, if dealing with important data, I'd add an odd disk to the
> array as a spare.


probably periodically mirror the raid onto a different non-raid system ???
> > and after its all said and done... pull out a disk (simulated disk crash)
> > and see if you're data is still intact
> Yep.  It's the only way to be sure.

and test again...

have fun

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