[linux-lvm] LVM cache/dm-cache questions.

[Ondrej Kozina]

On 08/26/2016 04:01 PM, lejeczek wrote:
> whatever you might call it, it works, luks encrypting,
> opening & mounting @boot - so I only wonder (which was my
> question) why not cache pool LVs. Is it not supported...
> would be great if a developer sees this question, I'm not
> sure jut yet about filing a bug report.

In general LVM2 doesn't auto-activate or interpret unknown device types. 
LUKS header is considered unknown from LVM2 perspective. Simply put LVM2 
doesn't understand LUKS header data. Not sure what you tried to do with 
cache pool LV, but in my opinion any effort to encrypt (live or 
detached) cache pool LV may end with severe data corruption...

As of now I think you have in general two options:

a) encrypt both PVs because obviously if you only encrypt the origin PV 
you end up with decrypted plaintext data stored in cache pool. Probably 
this is the exact scenario you were about to avoid?

Unfortunately a) is suboptimal with regard to performance since you'd 
perform the encryption of data blocks twice.

Option b): encrypt the top level LV (the one constructed from both cache 
and origin LV). This way ciphertext would be stored twice in cache PV 
and origin PV but the encryption would be performed only once.

Regards
Ondrej