[linux-lvm] Very slow i/o after snapshotting

[Micky]

On a machine, where weekly snapshots are created for dumping raw data,
the overall disk i/o has drastically degraded to few megabytes per
second. It is quite random and so slow that commands freeze often.

I was using chunk size of 512K and same byte size with dd.

Is it quite common; I read that such freezes require a reboot. Is
there a way to avert?
What am I missing here?