What is the difference between the various ZODB blobstorage layouts?

Question

The ZODB blobstorage directory contains a .layout file with the string 'lawn', 'bushy'.

What is the difference between the various blob storage directory formats?

Answer 1

It is explained here: https://github.com/zopefoundation/ZODB/blob/master/src/ZODB/tests/blob_layout.txt

FTA:

====================== Blob directory layouts

The internal structure of the blob directories is governed by so called layouts. The current default layout is called bushy.

The original blob implementation used a layout that we now call lawn and which is still available for backwards compatibility.

Layouts implement two methods: one for computing a relative path for an OID and one for turning a relative path back into an OID.

Our terminology is roughly the same as used in DirectoryStorage.

It also explains the formats in detail.

Answer 2

You generally don't need to worry about the layout; lawn is there only for backwards compatibility.

If you do have a lawn layout blobstorage (you'll get a warning in the log if you do) and want to migrate to a bushy layout, use the migrateblobs script; here is a buildout part to create the script:

[migrateblobs]
recipe = zc.recipe.egg
eggs = ZODB3
entry-points = migrateblobs=ZODB.scripts.migrateblobs:main

Shut down any instances and ZEO servers, back up your blob storage and run the script on your blobstorage directory:

$ mv var/blobstorage var/blobstorage-lawn
$ bin/migrateblobs var/blobstorage-lawn/ var/blobstorage

var/blobstorage will then contain the migrated blobs using the bushy layout.