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

[Arne Vajhøj]

On 10/20/2024 9:10 PM, Lawrence D'Oliveiro wrote:
> 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.

Only if it can rely on a successful write not being lost.

>> 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.

Yes - it can.

It is not impacted by a system crash.

And with a power outage they have hours to get power back and get the
data written (I believe 72 hours battery power is common).

Arne