Bug #37590: api.vgcreate uses a PE size of 1G - ceph-volume - Ceph

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Bug #37590

closed

api.vgcreate uses a PE size of 1G

Added by Jan Fajerski over 7 years ago. Updated 8 months ago.

Status:

Resolved

Priority:

Normal

Assignee:

Target version:

% Done:

Source:

Backport:

Regression:

Severity:

3 - minor

Reviewed:

Affected Versions:

ceph-qa-suite:

Pull request ID:

34740

Tags (freeform):

Merge Commit:

239c4bc8f3c14f892656264789217b6b80e12982

Fixed In:

v16.0.0-6063-g239c4bc8f3

Released In:

v16.2.0~1197

Upkeep Timestamp:

2025-07-22T22:41:01+00:00

Description

Using such a large extend size leads to potentially unused space of just under 1G per devices.
Why was such a large PE size chosen?

Introduced by https://github.com/ceph/ceph/commit/4a1b97efc87f3df15a39a76de074b4791f3528ca

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Updated by Lars Marowsky-Brée about 7 years ago

I agree, a 1GiB size for extents doesn't make a lot of sense; that it makes reading LVM2 output easier to read when looking at extents is not really a good reason, and I'm not sure how it allows us to create larger LVs? (This limitations no longer applies for LVM2 format vs LVM1, no?)

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Updated by Alfredo Deza about 7 years ago

Is the problem here that this is not explained in more detail? Or is there a different issue that needs to be solved?

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Updated by Martin Weiss almost 7 years ago

Is there any news on this topic? Do we really plan to waste so much of available disk capacity on the LVM based setups?

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Updated by Alfredo Deza almost 7 years ago

There isn't anything different, we believe that the choice of 1GB for LVM extents made it an order of magnitude easier to calculate space available and the possible waste isn't significant enough to change back.

It becomes more of a problem on very small OSDs, but we aren't optimizing for that use case, so I would recommend pre-creating the LVs if using tiny OSDs is what is needed.

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