I think you just answered your own question; 2TB with about 1.5x dedup,
and only 1GB of RAM isn't going to work. ZFS will need to check the
dedup tables everytime you write, and if the dedup tables don't fit*
into 1/4 of RAM (or was it that ZFS only uses 3/4 of available RAM by
default, then dedup only uses 1/4 of that ZFS RAM? I forget!), then
there will be a lot of iops running as ZFS keeps having to read the
dedup tables from disk instead.
I had a similar system, AMD64 3000 (I think, or 3200) with 2GB and when
I bumped it up to 8GB write speed exponentially improved.
* There is some calculation you can go through to work out dedup
requirements for RAM, but the rough rule of thumb is 2GB (I'd even say
4GB or more, if it's a live/nearline system, versus a backup/archive
system) of RAM for every 1TB; and you likely still need to tweak
arc_meta_limit.
For a larger example, I have an archive server with 20TB RAIDZ3 (13x2TB
disks), 1.62x dedup with 10.8T used and 12.9T free, and 48GB of RAM,
where arc_meta_limit has been tweaked to use 32GB of RAM instead. I get
about 20-30mbps (with dedup off I would normally be getting 50-60mbps)
over 1gbps ethernet.
On 24/08/2012 18:25, Julius Roberts wrote:
On 24 August 2012 15:03, Robbie Crash <sardonic.smi...@gmail.com> wrote:
Are you using compression or dedup on the FS?
Yes, both. We're getting about 1.5x dedup on the Backups pool, not
sure how to calculate compression
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