New User, new server

Warren Block wblock at
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.

More information about the freebsd-questions mailing list