Simulating bad sectors on file based storage device. How?

[Ravi Pokala]

-----Original Message-----
Date: Tue, 16 Feb 2021 16:05:03 +0300
From: Artem Kuchin <artem at artem.ru>
To: Alan Somers <asomers at freebsd.org>
Cc: freebsd-fs <freebsd-fs at freebsd.org>
Subject: Re: Simulating bad sectors on file based storage device. How?
Message-ID: <46b52475-385f-5931-f425-fd546dd5b377 at artem.ru>
Content-Type: text/plain; charset=utf-8; format=flowed

    gnope only allows to set probability, but i need an exact block in an 
    exact place.

ATA, NVMe, and SCSI all have commands to mark specific ranges of logical sectors as unreadable.

- ATA: WRITE_UNCORRECTABLE_EXT (has both report-failure-instantly and perform-real-error-recovery-before-reporting-failure modes)

- NVMe: Write Uncorrectable

- SCSI: WRITE_LONG (has both report-failure-instantly and perform-real-error-recovery-before-reporting-failure modes)

The base system does not contain programs to issue those commands specifically, but the commands can be assembled by hand and sent to the drive via `camcontrol cmd' (ATA, SCSI) or `nvmecontrol io-passthru' (NVMe). Obviously, assembling those commands would require spending some time with the ATA specs from t13.org, the NVMe specs from nvme.org, or the SCSI "Block Commands" spec from t10.org.

It should go without saying that those commands are dangerous, because by definition they destroy data. Use with caution after deep study of the docs in question.

-Ravi (rpokala@)


    15.02.2021 20:44, Alan Somers ?????:
    > If you have SCSI disks, you can inject errors with `sysctl 
    > kern.cam.da.0.error_inject`.? If not, you can use gnop(8) to simulate 
    > a flaky disk.
    >
    > On Mon, Feb 15, 2021 at 10:36 AM Artem Kuchin <artem at artem.ru 
    > <mailto:artem at artem.ru>> wrote:
    >
    >     Hello!
    >
    >     Is there a way to build a file base storage device (for example, file
    >     based zfs mirror) and then simulate a bad sector for one of the
    >     mirror
    >     sides?
    >
    >     Artem