Drive Caches (Re: Is Parallel Programming Hard, ...)

On 2025-05-23, Stefan Monnier <monnier@iro.umontreal.ca> wrote:

I don't understand what you're getting at, here.
I think Waldek's argument is that 256MB corresponds approximately
to the amount of data stored in 80-150 tracks, and seek time doesn't
change that fact.
>
IIUC, for SATA drives, NCQ is still limited to 32 in-flight commands, so
unless the drive is allowed to do write-back caching it seems the amount
of space used for write-buffering is likely small (compared to 256MB).
[ Unless it is common for individual write commands to cover multi-MB
  chunks of data?  ]

As I see it, with variable track length geometries, the OS file
system cannot make reasonable assumptions about track boundaries, so it
cannot maintain track/cylinder caches, but the drive processor can.

...
but HDDs are pretty damn expensive beasts nowadays (because prices have
not gone down for the last 10 years or so), so I guess that makes
the relative cost of 512MB of DRAM "negligible"?

Actually, HDDs are still on a steep downward price curve. The amount of
HDD space you get for USD 100 keeps going up, up, up. Look at portable
backup drives.