[pve-devel] Default cache mode for VM hard drives

[Cesar Peschiera]

> Cache=none means no host cache but backend cache is still in use. In case
> of DRBD this is a buffer in DRBD. So O_DIRECT return OK when data
> reaches this buffer and not RAID cache.

Excuse me please if i intervene in this conversation, but as i understand, 
if the data is in a buffer of DRBD, then DRBD must know that there exist 
data to replicate, so obviuosly the problem isn't in the upper layers (KVM, 
any buffer in the RAM controlled by some software, etc.), so the buffer of 
DRBD should be optimized according to convenience.

Moreover, DRBD have several Web pages that tell us with great detail about 
of optimize many things, including the configuration of his buffers for 
avoid the data loss, also with examples of with and without a RAID 
controller in the middle. So it, the softwares that are in the upper layers 
nothing can do about since that DRBD takes the control of the data as also 
of his own buffer.