Mailinglist Archive: opensuse (1470 mails)

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Re: [opensuse] Why Is Leap 42.1 Benchmarking Poorly?
  • From: Vojtěch Zeisek <vojtech.zeisek@xxxxxxxxxxxx>
  • Date: Thu, 25 Feb 2016 13:29:53 +0100
  • Message-id: <7358415.sGiNCtJ6JO@veles>
Dne Čt 25. února 2016 15:09:03 jste napsal(a):
btrfs does not do any copy on write. It does "redirect on write" which „Btrfs is a new copy on
write (CoW) filesystem for Linux...“ Did I misunderstand something? :-)

No; whoever created this page used confusing name. CoW snapshots
existed long before btrfs was invented and has quite precise meaning
in storage world - it is technology when old data is *copied*
elsewhere before being overwritten by new data in place. btrfs does
not overwrite old data ever - new data is written in free space,
leaving old intact. This applies not only to user data, but to
metadata as well - so you get completely new filesystem tree, and only
when this tree is constructed, the top level pointer is "flipped".

OK, thank You for clarification.

Client access is what is counted, right? ;-)

Is it sarcasm? Database exists to serve clients and if clients are cut
off for hours or days to perform backup, then yes, it counts. Or if
clients must wait for days to revert to older date because someone
made an error.

No, no sarcasm. The discussion is getting cycled here. Going back. If feature
called "CoW" in Btrfs is slowing down DB (doesn't matter in which step), then
it is not good for DB (at least now without extra tuning). Do all we agree on
that? I don't want to discuss details of DB/FS settings, backups and restores
of huge DBs. It can change the situation, right?

:) ) *and* revert to them in seconds for multiterabyte database (in
order of several dozens TB) without using snapshots I am all ears.

I don't say it is a bug. It just isn't the best for all user cases...

You said "it does not make sense". It is very far from "isn't the best
in all user cases".

OK, again. If some feature of Btrfs is making performance problems for DBs (do
we agree it does?), then it does not make sense to use it for DB, doesn't it?
Of course, there are dozens of user cases. Some are are suitable, some not.

Vojtěch Zeisek

Komunita openSUSE GNU/Linuxu
Community of the openSUSE GNU/Linux
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