linux-kernel - Re: [PATCH 1/1] hwmon: Driver for temperature sensors on SATA drives

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Message-ID: <yq1tv5zhdn5.fsf@oracle.com>
Date:   Mon, 16 Dec 2019 21:47:10 -0500
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-hwmon@...r.kernel.org, Jean Delvare <jdelvare@...e.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
        Chris Healy <cphealy@...il.com>
Subject: Re: [PATCH 1/1] hwmon: Driver for temperature sensors on SATA drives

Guenter,

> Not sure I understand what you mean with 'bazillions of sensors' and
> 'sensor per scsi_device'. Can you elaborate ? I see one sensor per
> drive, which is what I would expect.

Yes, but for storage arrays, hanging off of struct scsi_device means you
would get a sensor for each volume you create. Even though you
presumably only have one physical "box" to monitor (ignoring for a
moment that the drives inside the box may have their own sensors that
may or may not be visible to the host).

Also, multi-actuator disk drives are shipping. They present themselves
to the host as a target with multiple LUNs. Once again you'll probably
have one temperature sensor for the physical drive but many virtual
disks being presented to the OS. So you'd end up with for instance 4
sensors in hwmon even though there physically only is one.

It's a tough call since there may be hardware configurations where
distinct per-LUN temperature is valid (some quirky JBODs represent disk
drives as different LUNs instead of different targets, for instance).

How expensive will it be to have - say - 100 hwmon sensors instantiated
for a drive tray?

-- 
Martin K. Petersen	Oracle Linux Engineering