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

[Lawrence D'Oliveiro]

On Sat, 19 Oct 2024 21:31:51 -0400, Arne Vajhøj wrote:

> On 10/19/2024 9:25 PM, Lawrence D'Oliveiro wrote:
>>
>> On Sat, 19 Oct 2024 21:22:08 -0400, Arne Vajhøj wrote:
>>>
>>> On 10/19/2024 9:04 PM, Lawrence D'Oliveiro wrote:
>>>>
>>>> Here’s another question: why does a disk controller need a battery-
>> backed-
>>>> up cache? Or indeed any cache at all?
>>>
>>> Better performance.
>> 
>> Think about it: the OS already has a filesystem cache in main RAM. That
>> runs at main RAM speeds. Whereas the disk controller is connected
>> through an interface to the CPU suitable only for disk I/O speeds. So
>> any disk controller cache is on the wrong side of that interface.
> 
> That cache is toast if the system crashes. So applications
> that need to be sure data are written bypass that.

You can say the same for applications keeping data in their own RAM 
buffers. It’s a meaningless objection.