[Info-vax] Do any disks still lie about writing data to permanent storage ?

[chris]

On 07/06/21 14:28, Jan-Erik Söderholm wrote:
> Den 2021-07-06 kl. 15:04, skrev Simon Clubley:
>> Talking about disks has reminded me of something else.
>>
>> In the not too distant past, some disks lied about having written data
>> to permanent storage instead of merely to some internal cache that
>> would be lost on a power failure.
>>
>
> They did not lie, of course. They said that the data was in the cache,
> which was perfectly true.
>
>> Do any disks still lie about having committed data to permanent storage
>> or have we moved past that ?
>
> I would expect any modern SAN system to have extensive caching
> to reach good performance. Adn that the I/O finish when the data
> is in the cache.
>
> And why would the cache be lost at power failure?

Unless the cache has battery backup, all cache data will be lost on
power fail. Most have, but that only provides a limited time
to flush out to disk, typically minutes and that needs the drives
spunup and online to work.

Most modern drives have a large on board cache and that will be lost
on power fail, unless the system has a UPS. There are advantages for
cache, but it needs other system support to work properly...

>
> I think that your way of putting your question is "questionable".
>
>