[ZFS] Using SSD with partitions

[Jeremy Chadwick]

On Mon, Oct 17, 2011 at 11:53:43PM -0400, Patrick Donnelly wrote:
> Since people have asked about more details for my system:
> 
> It uses old desktop hardware with 5 1TB WD Caviar Blues in a raidz
> configuration with 1 of those drives being a hot spare (4 1TB drives
> in the raidz). The system currently has 2 GB of RAM IIRC.
> 
> I've been using NFS to access the data on my home network which has
> worked pretty well. Writing to NFS over my VPN from across the country
> is really bad which is one of the reasons I wanted to use a SSD for a
> ZIL. read/write performance overall tends to be bad though so I don't
> really know how much it will help. After fiddling around with NFS
> settings for a long time I soon gave up and instead use SSH when
> outside a LAN. That's another matter though and off-topic. :)

I don't see how using an SSD for ZIL is going to address issues of
latency and underlying network filesystems (not NFS but the idea of a
networked filesystem).  So many people think you can just throw a VPN
in between two locations and everything work will perfectly fine with
only nominal delays -- that isn't what happens at all at a packet level.
Network I/O tuning when a VPN is involved is a completely separate
topic.

NFS, by the way, is mainly intended to be used in very low-latency
environments (read: LANs).  You can fiddle with NFS and TCP window
settings all day and accomplish nothing considering cross-country
latency (within the US anyway) is around ~75ms on a good day.

When it comes to networked filesystems on UNIX, we have very little
choice.  NFS is the main one.  Then there's Stanford's Coda filesystem
thing, or maybe that's now part of AFS, I don't know.  Then there's
sshfs, which sounds wonderful until you realise all the dependencies and
nuances involved (mainly due to use of fuse, which we know on FreeBSD is
not so great).  Then there's Samba (CIFS/SMB, and now with Samba 3.6
offering SMB2 for Windows 7 clients), but that gets into issues of
security and cannot be forwarded via SSH (e.g. VPN would be needed)
given all its protocol some of which are UDP (not sure what the state of
NetBIOS is).

And none of this even begins to touch base on resiliency/reliability.
I have to remind people on a weekly basis that the Internet *truly* is
broken 24x7x365.  It cannot be relied upon 100% of the time, or even 90%
of the time.  VPN, SSH, plain-text packets... none of it matters when
the backbone carriers don't take the Internet seriously (and most do
not; it's still a best-effort service, at least that's how it's treated
by NOCs and technicians).

So what I'm saying is: I wish you luck in your endeavour to find
something that works for you.  In general I find SSH to be the most
convenient -- easy to deal with on a firewall level, authentication that
makes sense, and is easily manageable in general.  You might try making
use of things like Compression=yes in SSH as well.

If you find an SSD that is able to solve all of these problems, let me
know and I'll invest in one.  It'll be the first SSD with an RJ45 port
I'm sure.  :-)

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                   Mountain View, CA, US |
| Making life hard for others since 1977.               PGP 4BD6C0CB |