Discussion:
Arc, memory pressure and NFS
aurfalien
2013-11-15 18:40:10 UTC
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Hi,

Curious if Arc will reduce efficiently and quickly enough during NFS needs?

I've a rather large NFS server in terms of client needs and feel that i should limit Arc.

I'm coming off a black box scale up NAS (vendor shall remain nameless as there mention makes me ill) so I'm unsure how much NFS will be thrashed.

Given a decent amount of RAM at 256GB, should I ensure 25% for NFS by limiting arc max or depend on memory pressure for arc to back off?

Obviously testing will determine the proper course but I wanted some guidance in advance,

So, thanks in advance :)

- aurf
Berend de Boer
2013-11-15 19:02:42 UTC
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aurfalien> Given a decent amount of RAM at 256GB, should I ensure
aurfalien> 25% for NFS by limiting arc max or depend on memory
aurfalien> pressure for arc to back off?

Good question. I have simply allocated all memory to ZFS, assuming it
can do the caching better than NFS.

Eager to see the responses.

--
All the best,

Berend de Boer




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Richard Elling
2013-11-15 19:51:00 UTC
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Post by aurfalien
Hi,
Curious if Arc will reduce efficiently and quickly enough during NFS needs?
I've a rather large NFS server in terms of client needs and feel that i should limit Arc.
I'm coming off a black box scale up NAS (vendor shall remain nameless as there mention makes me ill) so I'm unsure how much NFS will be thrashed.
Given a decent amount of RAM at 256GB, should I ensure 25% for NFS by limiting arc max or depend on memory pressure for arc to back off?
Obviously testing will determine the proper course but I wanted some guidance in advance,
Are you running ZFS on the NFS server or client?
NFS server doesn't cache, it uses the underlying file system.
-- richard

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Schlacta, Christ
2013-11-15 20:05:12 UTC
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There have been some improvements in terms of arc reclaim and arc external
fragmentation, but I'd still say initially to limit your arc to 50%
explicitly, then observe it.and scale up or down as needed.
Post by aurfalien
Hi,
Curious if Arc will reduce efficiently and quickly enough during NFS needs?
I've a rather large NFS server in terms of client needs and feel that i should limit Arc.
I'm coming off a black box scale up NAS (vendor shall remain nameless as
there mention makes me ill) so I'm unsure how much NFS will be thrashed.
Given a decent amount of RAM at 256GB, should I ensure 25% for NFS by
limiting arc max or depend on memory pressure for arc to back off?
Obviously testing will determine the proper course but I wanted some guidance in advance,
So, thanks in advance :)
- aurf
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