CF Card wear optimalisation for ext4

[Bodo Thiesen]

* Andreas Dilger <adilger at dilger.ca> hat geschrieben:

> The "lifetime writes" value has not been around forever, so if the
> filesystem was originally created and populated on an older kernel
> (e.g. using ext3) it would not contain a record of those writes.

It was created as stable ext4 in the first place. So only if there was a
stable ext4 release which didn't update the "lifetime writes" value this
could be the case.

> There is also some potential loss if the filesystem isn't unmounted
> cleanly.

Yea, that *might* be it - but that only supports my statement, that this
value is mainly bogus.

> It definitely _can_ be used to monitor the writes to a particular
> filesystem over the past 24h, which is what the original poster was
> asking about.

Since it never get's updated unless the file system is unmounted, it can
only be used for a 24 hours test by mounting the file system now,
unmounting it 24 hours from now and then taking the difference.

Also the value is only available in granularity of 1 GB (plus minus
512MB) - at least in my case.

So, in any case, I wouldn't trust that value for any purposes at all.

I did test /sys/fs/ext4/sda/lifetime_write_kbytes now, that seems to be
somewhat less bogus, so *that* might actuall be usable for the 24 hours
test. But I wasn't talking about that when I said, that this lifetime
thing is bogus.

Regards, Bodo