2011-05-17 6:32, Donald Stahl пишет:
I have two follow up questions:
1. We changed the metaslab size from 10M to 4k- that's a pretty
drastic change. Is there some median value that should be used instead
and/or is there a downside to using such a small metaslab size?
2. I'm still confused by the poor scrub performance and it's impact on
the write performance. I'm not seeing a lot of IO's or processor load-
so I'm wondering what else I might be missing.
I have a third question, following up to the first one above ;)
3) Is the "4k" size anyhow theoretically based?
Namely, is it a "reasonably large" amount of eight or so
metadata blocks of 512Kb size,or something else is in
play - like a 4Kb IO?
In particular, since my system uses 4Kb blocks (ashift=12),
for similar benefit I should set metaslab size to 32k (4K*8
blocks) - yes/no?
Am I also correct to assume that if I have a large streaming
write and ZFS can see or predict that it would soon have to
reference many blocks, it can allocate a metaslab larger
that this specified minimum and thus keep fragmentation
somewhat not extremely high?
Actually, am I understanding correctly that metaslabs are
large contiguous ranges reserved for metadata blocks?
If so, and if they are indeed treated specially anyway,
is it possible to use 512-byte records for metadata even
on VDEVs with 4kb block size configured by ashift=12?
Perhaps not today, but as an RFE for ZFS development
(I posted the idea here https://www.illumos.org/issues/954 )
Rationale: Very much space is wasted on my box just to
reference data blocks and keep 3.5kb of trailing garbage ;)
4) In one internet post I've seen suggestions about this
value to be set as well:
set zfs:metaslab_smo_bonus_pct = 0xc8
http://www.mail-archive.com/zfs-discuss@opensolaris.org/msg40765.html
Can anybody comment - what it is and whether it would
be useful? The original post passed the knowledge as-is...
Thanks
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