Re: raid5/lvm setup questions

[David Greaves <david@dgreaves.com>]

Shane wrote:
> On Mon, Aug 07, 2006 at 08:57:13PM +0100, Nix wrote:
>> On 5 Aug 2006, David Greaves prattled cheerily:
>>> As an example of the cons: I've just set up lvm2 over my raid5 and whilst
>>> testing snapshots, the first thing that happened was a kernel BUG and an oops...
>> I've been backing up using writable snapshots on LVM2 over RAID-5 for
>> some time. No BUGs.
> 
> Just performed some basic throughput tests using 4 SATA
> disks in a raid5 array.  The read performance on the
> /dev/mdx device runs around 180mbps but if lvm is layered
> over that, reads on the lv are around 130mbps.  Not an
> unsubstantial reduction.
Check the readahead at various block levels
blockdev --setra xxx

I think I found the best throughput (for me) was with 0 readahead for /dev/hdX,
0 for /dev/mdX and lots for /dev/vg/lv

> 
> I seem to recall patches to md floating around a couple
> years back for partitioning of md devices.  Are those still
> available somewhere?
man mdadm and see --auto...

David


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