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Re: [linux-lvm] Sanity check: newbie wants strange LVM configuration



Joe,

Good plan, but I have some questions...

Joe Thornber wrote:

6) turn the 12G drive into a PV
7) extend the volume group with the new PV
8) create a striped logical volume big enough to hold the 12G

And LVM knows automagically to grab 12GB from the 40GB drive to stripe together into a 24GB drive?



OK so you should now have (40 - 6)G free on the big disk, and (12 -6)G free on the smallest disk.

Why don't I have 40-12 and 12-12 (nothing free on the smaller disk) resulting in a 24G raid0?


Also, I think it would be better to do the 16G first, then the 12G. Is there any reason why you did the 12G first, or is this interchangeable?


16) create a 16G striped LV

Shouldn't this be a 32G striped LV (16G from the 16G drive, another 16G from the 40G drive)?



You now have a striped LV 12G, a striped LV 16G + lots of left over
extents that can be added when needed.

Wouldn't that be a 24G striped LV and a 32G striped LV that I can append together into a 56G LV (and lots of non-striped extents that I can add to the end of that)?


Thanks for your help,

Chris

On Tue, Jan 02, 2001 at 10:22:34PM -0700, Chris Worley wrote:

I've got two disk drives, 12 & 16 GB IDE.  I'm adding a third 40GB
drive.  Time to start using LVM...

I want to get better performance, so, I'll put the 40GB drive on one
IDE controller, the other two drives on the second controller.  I'll
make two partitions on the 40GB drive that match the disk sizes of the
existing drives, and stripe each with it's match on the 40GB drive,
creating two raid0 arrays (one 12+12, and the other 16+16).  By
placing the dual-partitioned 40GB drive stand-alone on one IDE
controller, each striped with a partition/drive on the other
controller, any given file will only be striped across one partition
on each controller, so I should see the performance benefit of
striping (on IDE).

Should I use LVM or MD to do the striping (they both can do it, I was
just wondering which would be a better choice)?

Even if I use MD to stripe, I'd use LVM to append the two drives
together.

Before appending the drives, I'd make a temporary partition on the
40GB drive, and copy the current contents of the 16GB (/home) drive to
the temporary partition.  Then, I'd make the 16+16 raid0 a logical
volume, create a reiserfs on it, and copy the information back from
the temporary partition, to the new reiserfs.

Since the 12GB drive is the current root partition, it's a bit
trickier to copy.  I'd copy it's contents to a temporary partition on
the 40GB drive, boot from that temporary partition, then create the
second 12+12 raid0, and add it to the first logical volume, then
expand the reiserfs to cover both, copy the root file system from the
temporary partition to the new logical volume, and setup a reiserfs
root and boot.

Is this the correct approach for upgrading?

Finally, I'll have ~10GB unallocated on the 40GB drive.  I was
thinking of adding this to the end of the current logical volume (and,
again, expand the reiserfs to cover the additional space).

Since any file system looses performance when more than 90% full, this
final non-striped partition would be in a position where performance
would degrade anyway, and keep the raid0's in a position for full
performance.

Is that correct?

Sort of off-topic (not LVM related)...

I've got an IDE CDROM drive that I want to put on the same controller
as the 40GB drive.  I've been told that new UDMA drives do not have
the PIO performance hit associated with CDROM drives, so I should be
able to get full performance from my 40GB drive, even with a CDROM on
the same IDE controller.

Is that correct (or should I junk the IDE CDROM)?

Thanks,

Chris



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