New User, new server
wblock at wonkity.com
Wed Jun 21 13:45:10 UTC 2017
On Tue, 20 Jun 2017, Peter Ludikovsky wrote:
> 1) The new machine comes with a 128G SSD, in addition to the 2 4T HDDs
> from the older server. I'd like to set up ZFS root, with a slice of the
> SSD as ZIL and L2ARC, and the root mirrored across the SSD and the 2
> HDDs. Does this make sense, and if so what would be the ideal slice
> layout? Or should I just use the whole SSD as ZIL/L2ARC?
Don't mirror an SSD with hard drives. It will work, but cancels the
benefit of the SSD.
You don't say how much RAM the system has. Adding L2ARC without a
decent amount of RAM is actually worse than nothing. ZIL is built in.
An SSD to cache ZIL is called a SLOG. ZIL (and a SLOG) are for improving
the speed of synchronous writes. Generally, that is rare unless you are
using NFS and virtual machines. Also, a SLOG that is worthwhile usually
needs a low-latency SSD that is used exclusively for that purpose.
TLDR: unless you have at least 32GB or 64GB of RAM, adding L2ARC is
questionable. A SLOG is usually only helpful if you have lots of
synchronous writes, which is rare. Even then, it should be a fast,
dedicated SSD just for that.
> 2) Moving data from the old machine. Can I run zfs send/receive to get
> the ZFS on Linux datasets onto FreeBSD, or do I need to (r)sync?
zfs send | zfs recv usually works. It depends on the feature flags on
the originating system.
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