Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Lars Poulsen <lars@cleo.beagle-ears.com>
Newsgroups: comp.arch
Subject: Drive Caches (Re: Is Parallel Programming Hard, ...)
Date: Sun, 25 May 2025 20:55:43 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 24
Message-ID: <slrn10370uf.2e9bs.lars@cleo.beagle-ears.com>
References: <vvnds6$3gism$1@dont-email.me>
 <edb59b7854474033c748f0fd668badaa@www.novabbs.org>
 <w32UP.481123$C51b.217868@fx17.iad> <vvqdas$g9oh$1@dont-email.me>
 <vvrcs9$msmc$2@dont-email.me>
 <0ec5d195f4732e6c92da77b7e2fa986d@www.novabbs.org>
 <vvribg$npn4$1@dont-email.me> <vvs343$ulkk$1@dont-email.me>
 <vvtt4d$1b8s7$4@dont-email.me>
 <2025May13.094035@mips.complang.tuwien.ac.at>
 <vvuuua$1mt7m$1@dont-email.me> <vvvons$3uvs3$2@dont-email.me>
 <100oetb$c5c7$1@paganini.bofh.team> <100q47d$3k7s2$1@dont-email.me>
 <jwv8qmncayc.fsf-monnier+comp.arch@gnu.org>
Injection-Date: Sun, 25 May 2025 22:55:44 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="1af89e0c730aadc96d4f17c2d7449e15";
	logging-data="1650541"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/xeh0jQrrczAs+fMFRoxBx1chouGASD/c="
User-Agent: slrn/1.0.3 (Linux)
Cancel-Lock: sha1:aur+R6JpI6KkzcOsJnyigPNSnBM=
Bytes: 2580

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.