[Info-vax] RX2800 sporadic disk I/O slowdowns

[Lawrence D'Oliveiro]

On Sun, 20 Oct 2024 20:32:41 -0400, Arne Vajhøj wrote:

> On 10/20/2024 8:28 PM, Lawrence D'Oliveiro wrote:
>
>> Transaction resilience is a standard thing with databases (and
>> journalling filesystems) going back decades.
> 
> Yes.
> 
> But they can't do miracles.

They can ensure, to a high degree of confidence, that the on-disk 
structure is consistent. That is to say, each transaction is either 
recorded as completed or not recorded at all, nothing in-between.

> To be sure to come up ok after a system crash it is either write to
> plates or write to a cache that will survive the system crash (raid
> controller cache with battery backup).

Unfortunately, that controller cache can’t guarantee any of these things: 
it can’t do miracles either, all it does is add another point of failure.