Neil Brown wrote:
On Saturday May 9, goswin-v-b@xxxxxx wrote:
"NeilBrown" <neilb@xxxxxxx> writes:
On Sat, May 9, 2009 7:50 am, Goswin von Brederlow wrote:
So I still plan to offer a "--reserve-space=2M" option for mdadm to
allow the first 2M of each device to not used for raid data. Whether
any particular usage of this option is viable or not, is a different
question altogether.
How exactly would that layout be then?
Block 0 bootblock
Block 1 raid metadata
Block x 2M reserved space
Block x+2M start of raid data
Like this?
When using 1.2 metadata, yes, possible with bitmap
inserted between the reserved space and the start of raid data.
That realy seems to be the best option. Simple to implement, simple to
use and if mdadm copies the reserved space from old to new drives when
adding one it gives us exactly what we want.
Are you working on that already or do you think it needs more discussion?
Discussion is good....
I have just pushed out some changes to the 'master' branch of
git://neil.brown.name/mdadm
The last patch adds "--reserve-space=" support to create.
It only works with 1.x metadata (and causes the default to be 1.0).
You cannot hot-add a bitmap to a 1.1 or 1.2 array created with this
feature (the kernel cannot be told the right thing to do yet).
The space can have a K, M, or G suffix with the obvious meanings.
K is the default.
mdadm currently does not copy any data from one device to another.
This could possibly be added for "--add" but not for "--create".
Any reports of success or failure, or other comments would be most
welcome.
When using 1.0, it would be
Block 0..N-1 boot block and second stage
Block N..near-the-end raid data
Block x..y bitmap
block z superblock
I never liked the idea of 1.0.
What actualy does happen when you have raid on partitions and resize a
partition? Am I right that the raid then can't be assembled until the
raid itself gets grown (and the superblock gets moved to the new end)?
If you resize the partition under a 0.90 or 1.0 array, then md will
lose track of the metadata and you wont be able to assemble the array
again (there is nothing that will move it to the end).
How often do you resize a partition when there is data on it? I
suspect only when the partition is a logical volume. In that case 1.0
is awkward. In others it works fine.
Resizing a partition is not an issue, gparted does that nicely for the
case of partition with filesystem. But when the partition is part of a
raid array? I'm trying to think just how you would do that, other than
the very manual one partition at a time. I don't recall seeing gparted
documentation mentioning that. Perhaps LVM would do that, my use of it
is somewhat pedestrian and doesn't include swishing my data around like
mouthwash as I see some people do. As someone said in a movie, "I am not
a trusting person," and I don't trust LVM, possibly because of
experiences when it was new.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
"You are disgraced professional losers. And by the way, give us our money back."
- Representative Earl Pomeroy, Democrat of North Dakota
on the A.I.G. executives who were paid bonuses after a federal bailout.
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