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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.os.vms
Subject: Re: RX2800 sporadic disk I/O slowdowns
Date: Mon, 21 Oct 2024 03:27:56 -0000 (UTC)
Organization: A noiseless patient Spider
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On Sun, 20 Oct 2024 21:32:05 -0400, Arne Vajhøj wrote:

> On 10/20/2024 9:28 PM, Lawrence D'Oliveiro wrote:
>> 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?
> 
> Just that is is not lying when it says that it got it.

That’s not what it is saying. It is saying “write completed”.

> A system crash and restart will blank RAM and wipe out all OS
> and filesystem caches - it will not impact the cache in the
> RAID controller.

You hope.

You really are a believer in miracles, aren’t you?