description of how reads/writes work in detail

[calestyo]

Adding detailed descriptions of the following to the md(4) manpage:

• How reads/writes work in detail, especially with respect to the
  minimum/maximum number of bytes that are always fully read/written.
• How reads/writes work when the array is degraded and or when a rebuild takes
  place.
• Some general concepts of how the chunksize affect reads/writes.

Signed-off-by: Christoph Anton Mitterer mail@christoph.anton.mitterer.name

[calestyo]

Same as before: now directly as pull request.

And again, please thoroughly read what I've written and check it for any mistakes!

[calestyo]

Oh and one more thing:
Are those 4 KiB really hardcoded as such, or is actually the PAGE_SIZE? If the later I'd need to update this.

[neilbrown]

On Wed, 10 Jul 2013 07:13:46 -0700 Christoph Anton Mitterer
notifications@github.com wrote:

Same as before: now directly as pull request.

And again, please thoroughly read what I've written and check it for any mistakes!

---

Reply to this email directly or view it on GitHub:
#2 (comment)

Thanks. Again, it would be easier to reply if the patch was in the email.

• there are lots of typo speeling mistakes. Did you use a spell checker?
  mirroed deivces Fruther

• Please try to avoid \fB and \fP etc. Use.
  .B bold
  .BR "Bold followed immediately by a colon" :
  etc

• "reads\ /\ writes" - Is the really necessary? Why note "reads/writes"?

• You repeat the same parenthetical comment several times:
  obviously,
  +if any of the block layers above is not aligned with MD, even less will at most
  +be read\ /\ written

  which looks and sounds clumsy. Say it once and note that it applies to
  other levels, or something.

• Similarly you don't need to say "For example MD, dm-crypt ..." more than
  once.

• data will be IO distributedly read from the devices
  ^^^^^^^^^^^^^^^^^^^^^

Preferred language is English. I don't think above fits.

• RAID4/5/6 do use "PAGE_SIZE" rather than a literal "4K".
• are done blocks of
  ^in
• Saying "Failed devices won’t be used for reads\ /\ writes" is redundant
  even once. Saying it lots of times gets boring.
• The chunk size has no effect for the non-striped levels LINEAR
  not strictly true. The size of each device is rounded down to a multiple
  of the chunk size.
• .br should not be used to separate paragraphs. If you want a new
  paragraph, use ".P". If you don't, then don't. That is all.
• • For very large sequen...
  I'm sure there is a proper syntax for lists in 'man'. See mdadm.8 where I
  use
  .IP (bu 4

In general I think this content is probably useful. It need a bit of
cleaning up first though.

NeilBrown

[MrAta]

@calestyo would you please give a description of how and where the parities are updated in disks?