no, NFS by default does sync writes (at least unless you go to the effort of
configuring async writes on NFSv3)
As far as I know, turning sync on would only matter if you are worried about
having partial log messages on disk in the event of a crash.
enabing sync slows the output so that you will probably have fewer logs on disk
than if you didn't do sync, but you won't have a partial log.
Unless you also change all your queues to disk-only queues (which is VERY slow
compared to memory queues), you will still loose log messages in a crash,
sync=on doesn't protect you from this
So, by itself, there is very little reason to use sync=on, but if you were doing
full audit-grade logs (where you would rather have the system be unusable rather
than miss a single log message, and are willing to sacrafice 99% of your
performance to do so), sync=on is an indication that the system is configured
wrong.
David Lang
On Tue, 6 May 2014, Dave Caplinger wrote:
Perhaps if you are writing to a file that happens to be remote via NFS? With
async, the local filesystem buffer will report to rsyslog that it completed
the write successfully, but after that point the write via NFS may fail, and
now rsyslog will never know those messages never actually made it to disk on
the remote box..?
--
Dave Caplinger, Director of Architecture | Ph: (402) 361-3063 | Solutionary —
An NTT Group Security Company
On May 6, 2014, at 6:23 AM, Rainer Gerhards <[email protected]> wrote:
Sent from phone, thus brief.
Am 06.05.2014 11:36 schrieb "Thomas D." <[email protected]>:
Hi,
Rainer Gerhards wrote:
Besides, at least on a busy system, syncing is counter-productive. While
what is on the disk stays on the disk, the in-memory queue fills up more
rapidly. So in many use cases, activating sync potentially causes *more*
message loss.
[...]
Would you still recommend to enable syncing for important files like
"/var/log/auth.log" or not?
see above: definitely no
Interesting.
Just for my understanding: Could you describe a typical use case when
you would definitely want to set "Sync = on" for an action? Actual it
sounds like that there's never a reason...
I don't know one. Anyone else?
Rainer
Thanks!
-Thomas
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