Re: RX2800 sporadic disk I/O slowdowns

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.

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 ...

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.
Arne