They actually did have problems after standby-replay daemons took over
as active daemons. After each failover they had to clean up some stale
processes (or something like that). I'm not sure who recommended it,
probably someone from SUSE engineering, but we switched off
standby-replay and then the failover only took a minute or so, without
anything to clean up. With hot standby it took several minutes (and
cleaning afterwards). But the general recommendation is to not use
standby-replay anyway, so we follow(ed) that. But it still might be
useful in some scenarios, so proper testing is necessary.
Zitat von Александр Руденко <a.rudikk@xxxxxxxxx>:
IRC, last week during a Clyso
talk at Eventbrite I heard someone say that they deployed around 200
Filesystems or so, I don't remember if it was a production environment
or just a lab environment
Interesting, thanks!
I assume that you would probably be limited
by the number of OSDs/PGs rather than by the number of Filesystems,
200 Filesystems require at least 400 pools.
Sure, it's clear, thanks.
But it turned out that standby-replay didn't
help their use case, so we disabled standby-replay.
Interesting. There were some problems with standby-replay or they just do
not need "hot" standby?
чт, 21 нояб. 2024 г. в 11:36, Eugen Block <eblock@xxxxxx>:
I'm not aware of any hard limit for the number of Filesystems, but
that doesn't really mean very much. IIRC, last week during a Clyso
talk at Eventbrite I heard someone say that they deployed around 200
Filesystems or so, I don't remember if it was a production environment
or just a lab environment. I assume that you would probably be limited
by the number of OSDs/PGs rather than by the number of Filesystems,
200 Filesystems require at least 400 pools. But maybe someone else has
more experience in scaling CephFS that way. What we did was to scale
the number of active MDS daemons for one CephFS. I believe in the end
the customer had 48 MDS daemons on three MDS servers, 16 of them were
active with directory pinning, at that time they had 16 standby-replay
and 16 standby daemons. But it turned out that standby-replay didn't
help their use case, so we disabled standby-replay.
Can you show the entire 'ceph fs status' output? Any maybe also 'ceph
fs dump'?
Zitat von Александр Руденко <a.rudikk@xxxxxxxxx>:
>>
>> Just for testing purposes, have you tried pinning rank 1 to some other
>> directory? Does it still break the CephFS if you stop it?
>
>
> Yes, nothing changed.
>
> It's no problem that FS hangs when one of the ranks goes down, we will
have
> standby-reply for all ranks. I don't like that rank which is not pinned
to
> some dir handled some io of this dir or from clients which work with this
> dir.
> I mean that I can't robustly and fully separate client IO by ranks.
>
> Would it be an option to rather use multiple Filesystems instead of
>> multi-active for one CephFS?
>
>
> Yes, it's an option. But it is much more complicated in our case. Btw, do
> you know how many different FS can be created in one cluster? Maybe you
> know some potential problems with 100-200 FSs in one cluster?
>
> ср, 20 нояб. 2024 г. в 17:50, Eugen Block <eblock@xxxxxx>:
>
>> Ah, I misunderstood, I thought you wanted an even distribution across
>> both ranks.
>> Just for testing purposes, have you tried pinning rank 1 to some other
>> directory? Does it still break the CephFS if you stop it? I'm not sure
>> if you can prevent rank 1 from participating, I haven't looked into
>> all the configs in quite a while. Would it be an option to rather use
>> multiple Filesystems instead of multi-active for one CephFS?
>>
>> Zitat von Александр Руденко <a.rudikk@xxxxxxxxx>:
>>
>> > No it's not a typo. It's misleading example)
>> >
>> > dir1 and dir2 are pinned to rank 0, but FS and dir1,dir2 can't work
>> without
>> > rank 1.
>> > rank 1 is used for something when I work with this dirs.
>> >
>> > ceph 16.2.13, metadata balancer and policy based balancing not used.
>> >
>> > ср, 20 нояб. 2024 г. в 16:33, Eugen Block <eblock@xxxxxx>:
>> >
>> >> Hi,
>> >>
>> >> > After pinning:
>> >> > setfattr -n ceph.dir.pin -v 0 /fs-mountpoint/dir1
>> >> > setfattr -n ceph.dir.pin -v 0 /fs-mountpoint/dir2
>> >>
>> >> is this a typo? If not, you did pin both directories to the same
rank.
>> >>
>> >> Zitat von Александр Руденко <a.rudikk@xxxxxxxxx>:
>> >>
>> >> > Hi,
>> >> >
>> >> > I try to distribute all top level dirs in CephFS by different MDS
>> ranks.
>> >> > I have two active MDS with rank *0* and *1 *and I have 2 top dirs
like
>> >> > */dir1* and* /dir2*.
>> >> >
>> >> > After pinning:
>> >> > setfattr -n ceph.dir.pin -v 0 /fs-mountpoint/dir1
>> >> > setfattr -n ceph.dir.pin -v 0 /fs-mountpoint/dir2
>> >> >
>> >> > I can see next INOS and DNS distribution:
>> >> > RANK STATE MDS ACTIVITY DNS INOS DIRS CAPS
>> >> > 0 active c Reqs: 127 /s 12.6k 12.5k 333 505
>> >> > 1 active b Reqs: 11 /s 21 24 19 1
>> >> >
>> >> > When I write to dir1 I can see a small amount on Reqs: in rank 1.
>> >> >
>> >> > Events in journal of MDS with rank 1:
>> >> > cephfs-journal-tool --rank=fs1:1 event get list
>> >> >
>> >> > 2024-11-20T12:24:42.045056+0300 0xc5c1cb UPDATE:
>> (scatter_writebehind)
>> >> > A2037D53
>> >> > 2024-11-20T12:24:46.935934+0300 0xc5c629 SESSION: ()
>> >> > 2024-11-20T12:24:47.192012+0300 0xc5c7cd UPDATE: (lock inest
>> accounted
>> >> > scatter stat update)
>> >> > 2024-11-20T12:24:47.904717+0300 0xc5ca0b SESSION: ()
>> >> > 2024-11-20T12:26:46.912719+0300 0xc5ca98 SESSION: ()
>> >> > 2024-11-20T12:26:47.910806+0300 0xc5cc3c SESSION: ()
>> >> > 2024-11-20T12:27:35.746239+0300 0xc5ccc9 SESSION: ()
>> >> > 2024-11-20T12:28:46.923812+0300 0xc5ce63 SESSION: ()
>> >> > 2024-11-20T12:28:47.903066+0300 0xc5d007 SESSION: ()
>> >> > 2024-11-20T12:29:08.063326+0300 0xc5d094 EXPORT: ()
>> >> > di1/A2037D53
>> >> > 2024-11-20T12:30:46.909621+0300 0xc5d96f SESSION: ()
>> >> > 2024-11-20T12:30:47.908050+0300 0xc5db13 SESSION: ()
>> >> > 2024-11-20T12:32:46.907649+0300 0xc5dba0 SESSION: ()
>> >> > 2024-11-20T12:32:47.905962+0300 0xc5dd44 SESSION: ()
>> >> > 2024-11-20T12:34:44.349348+0300 0xc5ddd1 SESSIONS: ()
>> >> >
>> >> > But the main problem, when I stop MDS rank 1 (without any kind of
>> >> standby)
>> >> > - FS hangs for all actions.
>> >> > Is this correct? Is it possible to completely exclude rank 1 from
>> >> > processing dir1 and not stop io when rank 1 goes down?
>> >> > _______________________________________________
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>> >>
>> >>
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>>
>>
>>
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