Dne 12. 10. 24 v 0:46 Drew Eckhardt napsal(a):
What's the lvm2/dm-thin snapshot memory and disk overhead for each
chunk (default 64k) overwritten?
Hi
Depends on the usage.
If you write full 64K block - the whole new provisioned chunk is written.
If you write 1st. 4K block to 'not yet provisioned' chunk for snapshot - then
remains of 64-4 of the origin chunk to be 'copied' to this newly provisioned
chunk.
If you write to already provisioned chunk for a snapshot thin LV - nothing is
copied and all goes just the this chunks.
When origin 'write' to a chunk shared with 'snapshot' - then snapshot will
keep the unmodified chunk and origin gets a new copy with updated content.
Note - snapshot thin LV is just like any other 'thin LV' - it just 'shares'
already allocated chunks with its origin.
Simply said - writing task always 'pays' the price with block update...
Hopefully this makes it clear.
Regards
Zdenek
PS: it's way more efficient compared with old 'thick' snapshots...
