Michelle Sullivan michelle at sorbs.net
Tue Apr 30 14:12:58 UTC 2019

Michelle Sullivan
Sent from my iPad

> On 01 May 2019, at 00:01, Alan Somers <asomers at freebsd.org> wrote:
>>> Unfortunately however there is also cache memory on most modern hard
>>> drives, most of the time (unless you explicitly shut it off) it's on for
>>> write caching, and it'll nail you too.  Oh, and it's never, in my
>>> experience, ECC.
> Fortunately, ZFS never sends non-checksummed data to the hard drive.
> So an error in the hard drive's cache ram will usually get detected by
> the ZFS checksum.

True, but a drive losing power mid write will ensure the checksum doesn’t match the data (even if it is written before the data)... you need to ensure all the data and the checksum is written before drive power down.. and in the event of unexpected hard power fail, you can’t guarantee this.  Battery backup in the controller that has a write cache and re-writes the last few writes on power restore on the otherhand will save you.. which is why the other machine at my disposal hasn’t failed to date.


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