[linux-lvm] Reattach cache

[Xen]

Ehm,

When you split a cache and later reattach it, LVM ensures it is in a
consistent state right?

LVM is a bit old, I mean Ubuntu 16.04 version, so something about 133.

[matthew patton]

by definition when you detach a cache it is now entirely invalid and will (should) be treated as empty.

[Xen]

Post by matthew patton
by definition when you detach a cache it is now entirely invalid and
will (should) be treated as empty.

Yeah but it wasn't.

Within seconds the rootfs was readonly and because I was running some
apt thing at the same time, now a large bunch of packages became
corrupted in the apt index (dpkg index).

A bunch are still missing md5 files but I am on limited bandwidth so not
reinstalling.

So I assumed the above that you write.

But it bit me once more.

[Zdenek Kabelac]

Post by Xen
Ehm,
When you split a cache and later reattach it, LVM ensures it is in a
consistent state right?
LVM is a bit old, I mean Ubuntu 16.04 version, so something about 133.

Hi

Sorry but version 133 is really ancient - the original purpose of 'cache'
--splitcache was rather more debug oriented.

Clearing of cache-pool metadata when cache-pool is reattached to another LV
goes with version 2.02.162 - so your version is way too old...

In your case - just destroy the cache (--uncache) and do not try to reuse
cache-pool unless you really know what you are doing.

Regards

Zdenek

[Xen]

Post by Zdenek Kabelac
In your case - just destroy the cache (--uncache) and do not try to
reuse cache-pool unless you really know what you are doing.

But I still don't know how to clean the metadata manually.

[Zdenek Kabelac]

Post by Xen

Post by Zdenek Kabelac
In your case - just destroy the cache (--uncache) and do not try to
reuse cache-pool unless you really know what you are doing.

But I still don't know how to clean the metadata manually.

Just drop/lvremove the cache-pool and create the new one again.
There is no specific 'zeroing' metadata command.

And as said - newer tool will ZERO by default and you need to pass -Zn to
avoid zeroing (in case you want to reattach same cache-pool to unused data -
but as said you need to be skilled user knowing what you are doing for this
use case)

Zdenek