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

[Lawrence D'Oliveiro]

On Sun, 20 Oct 2024 21:17:06 -0400, Arne Vajhøj wrote:

> 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.

In other words, that the disk controller is not lying to you when it says 
a write has completed?

>>> 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.

Now you are really starting to sound like a believer in miracles ...