[linux-lvm] calculating size of metadata.

[Jan-Hendrik Palic]

Hi,

On 24.04.2012 16:52, Ray Morris wrote:
> It's good think about this because running out of metadata space is no
> fun.

We had this problem already on an other system. We had to migrate to 
another storage with pain. The new storage has a larger space for the 
metadata for sure. .-)

But I want to understand and not only set this size to an high value. 
Therefore this question here.

> We use 181KB for about 300 LVs, where each snapshot is counted as
> two LVs because of the way it's stored.  That's based on the size of the
> backup. vgs shows 8 MB of metadata used, though:
>
> # vgs --units k -o vg_mda_count,vg_mda_free,vg_mda_size clones
> vgs  #VMda VMdaFree  VMdaSize
> vgs      3  7973.50k 16444.00k

Thank you and Lars for your replies. If I understand you right, I have 
to look to the count of LVs I will have in the future and not only on 
the size of my volumegroup.

Ok.

> In any event, on a 19,950,000 MB partition, even 64 MB of metadata
> would represent 0.0006% of the storage. To think of it another way, 64
> MB costs roughly 0.03 cents, so allocate plenty.

Lars stated in his mail to this list, that one entry for a LV should be 
less than 1kb. So if I calculate 2kb for this entry, I will be safe. I 
checked this here and I can confirm this.

If I have a metadata space of 64MB, I am able to create 32000 different 
LV (without snapshots). Right?

Well, that is enought, even with snapshots,

Anyway ... thank you for my enlightment. .-)

Best regards

Jan