Re: RAID-1 possible for multi-filesystem disk?
Re: RAID-1 possible for multi-filesystem disk?
- Subject: Re: RAID-1 possible for multi-filesystem disk?
- From: "Jay A. Kreibich" <email@hidden>
- Date: Tue, 14 Sep 2004 22:14:23 -0500
On Tue, Sep 14, 2004 at 10:49:52PM -0400, Jack Howarth scratched on the wall:
> I know this may not be the most appropriate place to ask this
> question but I am wondering if any Darwin experts here know the
> limits of the current RAID-1 support in Panther. In particular, I
> am interested in creating a RAID-1 mirror using two identical SATA
> drives in a dual G5. I understand that a single filesystem disk
> can be non-destructively converted over to a unpaired mirror
> using the command...
>
> diskutil enableRAID mirror disk0
>
> Unfortunately this comamnd fails on a disk0 that contains two
> HFS+ partitions with an error message that the disk was not
> appropriate and an error number -9694.
The diskutil man page implies this isn't possible:
--------------------------------------------------
enableRAID mirror device
Convert single filesystem disk into a unpaired mirror RAID
set. Ownership of the affected disks is required.
--------------------------------------------------
I think they mean "Convert single-filesystem disk...". In other
words, it won't work for disks with more than one filesystem
(i.e. partition). I suppose they could mean "Convert one disk with
a filesystem", but that seems obvious.
> While I can understand that
> the current diskutil may have limitations on the enableRAID feature
> I am now wondering if MacOS X 10.3 supports RAID-1 of disks with
> multiple bootable partitions at all? Can anyone confirm that if
> I were to destructively repartition the drives and manually create
> the RAID-1 in DiskUtility (before reinstalling Panther) that I
> could in fact have both HFS+ partitions on a disk0 set up to mirror
> with RAID-1 on a second disk? I am a tad worried that I may have
> run into a nasty limitation of the OS's RAID support.
I'm guessing that is true. When you create a RAID set, you need to
give a filesystem type. Filesystems are associated with volumes
(i.e. partitions), not raw disks. So I'm fairly sure that a set of
mirrored disks is treated like a volume/partition, and not a raw disk.
That means you can't partition a RAID set.
This isn't that unusual for basic logical volume managers like the
software RAID system. I realize hardware RAIDs can do more advanced
things, but this is not a surprising limitation, even if it is a bit
frustrating for you.
-j, who's only mirrored whole disks.
--
Jay A. Kreibich | Comm. Technologies, R&D
email@hidden | Campus IT & Edu. Svcs.
<http://www.uiuc.edu/~jak> | University of Illinois at U/C
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