Re: FreeBSD + ZFS on a production server?

On Mon, 9 Jun 2008 23:31:35 +0200 (CEST),
Wojciech Puchar <wojtek@xxxxxxxxxxxxxxxxxxxxxxx> said:

W> but why you need [a filesystem for linux that do checksum on the fly]?! all
W> PATA/SATA drives do checksumming on every read. in hardware, no CPU load.

These days, hardware isn't just hardware. A disk drive can have around
300,000 lines of low-level firmware, and who wants to bet that it's
completely bug-free? Silent-write errors are actually a big problem:

http://www.usenix.org/publications/login/2008-06/openpdfs/bairavasundaram.pdf
An Analysis of Data Corruption in the Storage Stack

"In this paper, we present the first large-scale study of data corruption.
We analyze corruption instances recorded in production storage systems
containing a total of 1.53 million disk drives, over a period of 41 months.
We study three classes of corruption: checksum mismatches, identity
discrepancies, and parity inconsistencies. We focus on checksum mismatches
since they occur the most; more than 400,000 instances of checksum
mismatches over the 41-month period."

--
Karl Vogel I don't speak for the USAF or my company

Mangled song lyric: Looks like tomatoes
Actual lyric: Looks like we made it. (Barry Mannilow)
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