DM Performance

DM Performance

[Tom Parker]

I'm trying to find out whether there's been any work regarding device mapper 
with very large mapping tables. Specifically,

1) Is there any limit on the size of a mapping table? Can hand over a table with 
30,000+ entries and expect DM to still work?
2) Is there any significant performance degredation with large tables?
3) As I understand it, DM stores the mapping tables itself somehow, in a way 
that is persistant across reboots. I'm not certain about that, but if that's so, 
wouldn't it also create limits on table sizes? If not, are there any suggested 
ways to make complex/large tables persistant?

Thanks,

Tom Parker
-- 
palfrey@tevp.net - http://tevp.net
Illegitimus non carborundum

Re: DM Performance

[Alasdair G Kergon]

On Thu, Apr 07, 2005 at 02:29:20PM +0200, Tom Parker wrote:
> 1) Is there any limit on the size of a mapping table? Can hand over a table 
> with 30,000+ entries and expect DM to still work?

Yes, but you might hit hard-coded libdevmapper limit.

> 2) Is there any significant performance degredation with large tables?

Should not be.

> 3) As I understand it, DM stores the mapping tables itself somehow, in a 
> way that is persistant across reboots. 

No, that's one thing lvm2, multipath-tools etc. are for.

Alasdair
-- 
agk@redhat.com