(Re ** 6)[1]: Extending "thin_trim" (about pseudo-raid: Why!)

["Thomas Brücker" <public0x05bf@xxxxxxxxxx>]

Dear Mr. Kabelac,

* I have had two (real!) cases which three mechanical harddisks, that have
had defective sectors (within warranty time!), not just announced as
defective, but really unreadable.

1st case: Two ecolocical, energy saving samsung disks, that have both got
unreadable sectors, happyly mutually not on the same location, connected
as raid1: All data could be read and saved.

2nd case: An usb-disk that had got unreadable sectors with a 'pseudo-raid'
on it: All data could be read and saved.

* Experimental case: Test of 'pseudo-raid' on a dvd, the dvd was scratched
and could partially not be read: The pseudo raid could be read without any
problem (
* ok. if the metadata on the dvd, which is responsible to have access to
  the dvd at all, is scratched, you loose everything.
* about a read-only!-dvd with 'raid' on it ...: I use another 'strange'
  construct with dm-target dm-snapshot to protect the dvd from writing to.
).

* I have had at least two (real) cases of harddisks with each having a
unreadable first sector (== the partition table): The laptops could
neither
been started, nor could the data.been accessed, After rewriting the
partition table, the disks worked just long enough, to copy a complete
image of them.
(either the disk has a partiton at the 'usual' location, or you may search
for the begin of the filesystem...)

* Link (I don't want to attach and clutter your mail server with unneces-
  sary images) to: Defective disk in harddisk device.
  "http://www.thomas-r-bruecker.ch/favorites/io/disk/Defective_disk.jpg";.
  (It begins mostly with defective sectors and ends in a crash.)

* So, for me, it is a good idea, to protect myself from defective sectors.

* 'Normal' raid(1):
  * notebooks with two harddisks in it ...?
  * travelling with a laptop and two usb-harddisks ...?


Sincerely

Thomas

============================================================================
On Tue, November 19, 2024 2:37 pm, Zdenek Kabelac wrote:
> Dne 19. 11. 24 v 3:11 "Thomas Bruecker" napsal(a):
>> ]...]

> [...]
> And while I can 'see' a small value in having the same data stored
> multiple times on the same drive - the protection you get from this is
> close to nothing
> [...]
> With prices of storage these days I'd simply recommend to simply use the
> raid the way it's supposed to be used.
> [...]