[TUHS] Is it time to resurrect the original dsw (delete with switches)?

Theodore Ts'o tytso at mit.edu
Mon Aug 30 21:56:39 AEST 2021

On Sun, Aug 29, 2021 at 08:36:37PM -0700, Bakul Shah wrote:
> Chances are your disk has a URE 1 in 10^14 bits ("enterprise" disks
> may have a URE of 1 in 10^15). 10^14 bit is about 12.5TB. For 16TB
> disks you should use at least mirroring, provided some day you'd want
> to fill up the disk. And a machine with ECC RAM (& trust but verify!).
> I am no fan of btrfs but these are the things I'd consider for any FS.
> Even if you have done all this, consider the fact that disk mortality
> has a bathtub curve.

You may find this article interesting: "The case of the 12TB URE:
Explained and debunked"[1], and the following commit on a reddit
post[2] discussiong this article:

   "Lol of course it's a myth.

   I don't know why or how anyone thought there would be a URE
   anywhere close to every 12TB read.

   Many of us have large pools that are dozens and sometimes hundreds of TB.

   I have 2 64TB pools and scrub them every month. I can go years
   without a checksum error during a scrub, which means that all my
   ~50TB of data was read correctly without any URE many times in a
   row which means that I have sometimes read 1PB (50TB x 2 pools x 10
   months) worth from my disks without any URE.

   Last I checked, the spec sheets say < 1 in 1x1014 which means less
   than 1 in 12TB. 0 in 1PB is less than 1 in 12TB so it meets the

[1] https://heremystuff.wordpress.com/2020/08/25/the-case-of-the-12tb-ure/
[2] https://www.reddit.com/r/DataHoarder/comments/igmab7/the_12tb_ure_myth_explained_and_debunked/

Of course, disks do die, and ECC and backups and checksums are good
things.  But the whole "read 12TB get an error", saying really
misunderstands how hdd failures work.  Losing an entire platter, or
maybe the entire 12TB disk die due to a head crash, adds a lot of
uncorrectable read errors to the numerator of the UER statistics.

It just goes to show that human intuition really sucks at statistics,
whether it's about vaccination side effects, nuclear power plants, or
the danger of flying in airplanes versus driving in cars.

	      	   	     	 	   - Ted

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