On Fri Oct 02, 2009 at 08:46:47AM -0700, Ben DJ wrote:
> keld@xxxxxxxx,robin@xxxxxxxxxxxxxxx
>
>
> Hi,
>
> 2009/10/2 Keld Jørn Simonsen <keld@xxxxxxxx>:
> > if the raid type happens to be the same layout as a non-raid partition, it
> > works. raid10,n2 default layout (ver 0.90) is equivalent with non-raid,
> > as the raid superblock is in the end of the partition.
>
> That makes sense, thanks. Not clear whether that's "officially
> supported" or "just lucky".
>
> Just to be ccertain, which metadata version, 0.90(default) or 1.0?
> According to the man page,
>
> 0, 0.90, default
> Use the original 0.90 format superblock. This format limits
> arrays to 28 component devices and limits
> component devices of levels 1 and greater to 2 terabytes.
>
> 1, 1.0, 1.1, 1.2
> Use the new version-1 format superblock. This has few
> restrictions. The different sub-versions store
> the superblock at different locations on the device, either at
> the end (for 1.0), at the start (for
> 1.1) or 4K from the start (for 1.2).
>
> it's v 1.0 that specifically states the super block is "at the end".
> Will either/both work?
>
Either 0.90 or 1.0 will work (both are held at the end)- 0.90 allows for
kernel auto-assembly, but is a legacy format. Any modern Linux
distribution will use an initrd which can assemble arrays with any
superblock, so current advice would be to use 1.0.
> On Fri, Oct 2, 2009 at 8:15 AM, Robin Hill <robin@xxxxxxxxxxxxxxx> wrote:
> > The main reason is that RAID-1 works across any number of disks (as
> > they're all identical) whereas RAID-10,nX working is an artifact of how
> > that layout works for X drives (they end up being identical to RAID-1).
>
> As X is a variable, according to the man page,
>
> "The number is the number of copies of each datablock. 2 is normal,
> 3 can be useful.
> This number can be at most equal to the number of devices in the
> array. It does
> not need to divide evenly into that number (e.g. it is perfectly
> legal to have an 'n2'
> layout for an array with an odd number of devices)."
>
> does "RAID-10,nX working is an artifact" hold true for any X?
>
Yes - RAID-10,nX for X disks will result in (effectively) a RAID-1
layout.
> If I've a 4-drive RAID-10 array that I want to have a bootable-/boot
> on, should X best be "normmal" 2, "useful" 3, or "unmentioned" 4? As
> usual it seems that performance, redundancy/robustness, and space
> utilization, as well as just being able to boot, all have a part to
> play.
>
For a boot partition I'd stick with RAID-1, then use RAID-10,f2 for
other partitions. There's no real advantage in using RAID-10,n4 over
RAID-1 (it's a different code-path so there may be slight differences
one way or the other, but nothing that will matter for a boot
partition anyway), and just makes the setup more unusual.
It's up to you though - RAID-10,n4 and a four-way RAID-1 will have the
same on-disk layout, so either will work fine. Oh - one other thing is
that RAID-1 is expandable (you can add other partitions later) whereas
RAID-10 is not currently.
Cheers,
Robin
--
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( ' } | Robin Hill <robin@xxxxxxxxxxxxxxx> |
/ / ) | Little Jim says .... |
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