On Sun, 2021-02-28 at 10:01 +0100, Guido Trentalancia wrote:

Many obsolete hard drives do not support the Synchronize Cache SCSI
command. Such command is generally issued during fsync() calls which
at the moment therefore fail with the ILLEGAL_REQUEST sense key.

It should be that all drives that don't support sync cache also don't
have write back caches, which means we don't try to do a cache sync on
them.  The only time you we ever try to sync the cache is if the device
advertises a write back cache, in which case the sync cache command is
mandatory.

I'm sure some SATA manufacturers somewhere cut enough corners to
produce an illegally spec'd drive like this, but your proposed remedy
is unviable: you can't ignore a cache failure on flush barriers which
will cause data corruption.  You have to disable barriers on the
filesystem to get correct operation and be very careful about power
down.

James