[linux-lvm] Sanity check: newbie wants strange LVM configuration
Chris Worley
cworley at liberate.com
Wed Jan 3 16:40:15 UTC 2001
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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