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I think Raid 5 need minimum 3 disks. if any one fail it start write the parity in the memory. It is applicable for harware-raid controller while that time the performence will go down while you reboot again in the boot up again it will start to regenerate parity. i think for sw/raid also it's doing the same thing only.
Originally Posted by amitpardesi
I am using mdadm to emulate s/w raid on my system.
I am trying to create a RAID 5 configuration on my system. I have 4 disks, each of X GB, with me. I can create a raid 5 by the following command:
In reality, the first command creates a raid 6 array, which does not really make sense when you have 4 drives total. if that setup gives you the space you need, it is probably safer to use raid10, for better redundancy. raid5 basically combines the speed of striping with the security of mirroring. unless your drives are old and likely to fail soon, (and if so, why do you use them for trusted storage) there is probably no need to keep a hot spare.
did you try to create a 2-disk raid5 array, or is it a question. my guess is that mdadm would either create a degraded 3-drive array or fail.
Normally the array will be started after it is assembled. However if
--scan is not given and insufficient drives were listed to start a com-
plete (non-degraded) array, then the array is not started (to guard
against usage errors). To insist that the array be started in this
case (as may work for RAID1, 4, 5 or 6), give the --run flag.
if each disk is 500GB (like mine) then RAID5 gives 1.5TB space where RAID10 gives 1TB
as im more instersted in the size avalable and speed increace that stripinfg gives but am not prepared with the one drive fails you loose everything aspect of RAID0
5 was the obvious choice at least that can withstand 1 of 4 failing without loss (but 2 failing kills the whole array) whereas with 10 one can fail, or 2 but not any 2