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Re: [linux-lvm] calculating size of metadata.



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


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