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From: "R. Schwartz" <schwrtz@protonmail.ch>
To: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Should nossd mount option be used for an HDD detected as non-rotational?
Date: Sat, 13 Jul 2019 09:22:20 +0000
Message-ID: <htetrjLP1jLMK9WTasfT2e5ZdkY1yV0iY3PHjVEDqCKIZ8d2VwdRTBRezsUAxzKawi_lsxBi5HYfOlvyByGPBwswTCKXSt_lbhRCAmQZ2Qg=@protonmail.ch> (raw)

My HDD (one partition, BTRFS) reports itself as non-rational:

    $ cat /sys/class/block/sda/queue/rotational
    0

According to btrfs(5), by default, BTRFS detects this value and turns on
SSD optimizations for the HDD. Naturally, I'm puzzled...

My question is: should I use the nossd mount option for the HDD?

Following is more details about this HDD.

It's a recent Western Digital Blue 2TB HDD, model WD20EZAZ. Given its
cache size is a rather large 256MB, some people say it's likely an SMR
(shingled magnetic record) HDD.

Since Host-Managed and Host-Aware SMR HDDs support the `REPORT_ZONES`
ATA/SCSI command, I ran this test using `sg3_utils`:

    # sg_rep_zones -R /dev/sda
    Report zones command not supported
    sg_rep_zones failed: Illegal request, Invalid opcode

Therefore, _if_ it's SMR, it must be Drive-Managed SMR.

So is there a good reason why the HDD reports itself as non-rotational?
Does it have to do with SMR?

Additioanlly, the HDD is connected through a SATA to USB connector. I
original suspected it was an issue with the connector, but I tested with
other HDDs with the same connector and they all report as rotational.


             reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-13  9:22 R. Schwartz [this message]
2019-07-13 11:06 ` Andrei Borzenkov
2019-07-13 11:18   ` R. Schwartz

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