[Gllug] RAID 1 and RAID 5

[Mike Brodbelt]

On Thu, 2002-12-05 at 02:35, Xander D Harkness wrote:
> Mike Brodbelt wrote:
> > 
> > Note that the contents of raidtab are pretty much ignored by everything
> > except mkraid - the details are written to the raid superblock, so after
> > the md device is created, raidtab becomes irrelevant. 
> Thanks - that explains why it will not accept another disk :-)
> 
> If I create a raid 5 array with 3 disks, may I add more and more disks 
> as long as I keep it raid 5?

No. A RAID5  array with n disks will use provide n-1 disks as space, and
1 as parity, though the parity is striped across the disks. Thus it's
not possible to add another disk to an existing RAID5, as it would
require rewriting all the stripes. Some good hardware RAID controllers
can do this, but the md driver can't.
 
> I am going to create a raid 5 with three disks.  My brother has finally 
> got upset enough to install RH8 over the XP (that he paid for) as he has 
> had to reinstall XP every day this week as it keeps failing.  It will 
> lose the od file here and there and then demand to be re-registered.
> 
> The second time after he requested a new number he started getting calls 
> from Microsoft and FAST requesting an appointment regarding licencing 
> issues......

Unbelievable....

Mike.


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