Using an SSD "disk" for /

[Jeremy Chadwick]

On Tue, Nov 02, 2010 at 01:31:24PM -0400, Mikhail T. wrote:
> I'm setting up a new system and would like to use a moderate (64Gb
> or 128Gb) SSD-drive to boot from.
> 
> This will house /, /var, /home, and the /usr/local and thus see
> plenty of activity, whenever src and ports are updated, or "world"
> is remade, or packages are upgraded. I'm hoping, these operations
> would be much faster, than with a regular HDD.
> 
> However, people mention, that SSDs develop /severe/ performance
> degradation if written to A LOT -- unless some SDD-specific
> operation (TRIM) is used, but not all Operating Systems support
> that... Does FreeBSD-8? Is that sufficient, or will an SSD degrade
> quickly anyway?
> 
> Does anyone use an SSD under FreeBSD? Which brand/model? Are you
> happy with it?
> 
> Also, what parameters should I give to newfs? SSDs' characteristics
> seem rather different from HDDs', so it is unlikely, that newfs'
> defaults will be optimal for an SSD... Would a different filesystem
> (ZFS?) be a better choice, than FFS, for these devices?

Yes, I use SSDs as the OS disk.  Depending on the system's needs, I use
one of the following models:

- Intel X25-V 40GB
- Intel X25-M 80GB

The reason I go with Intel disks is because they dominate all other SSD
brands when it comes to IOPS.  I'm less interested in sequential
throughput in this particular case.  I also go with Intel because I have
a pretty severe dislike for OCZ products (and that's my problem/issue
not yours).

I use UFS2 + softupdates on all filesystems on the SSDs (except for the
root filesystem, which lacks SU).  Those filesystems are /, swap, /usr,
/tmp, and /var.  I do not do any "tuning" of the filesystems either, so
I imagine there's room for speed improvements there as well.

As for the performance: it's something you'll have to see for yourself.
The performance is outright amazing when it comes to administrative
tasks (OS installation, newfs, massive copies of data to/from the SSD,
updating /usr/src and /usr/ports, etc.).  Try a build/install world or
kernel sometime on an SSD and watch your terminal.  You'll be pretty
impressed.

Our systems which use SSDs *always* have at least one mechanical HDD
included in the system (in fact usually 3, using ZFS raidz1).  These are
used for things like /var/mail and /home.

As for TRIM and the like -- yes, that's a concern of mine as well, but
for right now I just monitor the SSDs with smartmontools 5.40 and
smartctl -a.

If I had to make a recommendation of which drive to get, I would say get
a drive that offers at least 80GB.  I have to make some sacrifices with
the 40GB.  Having swap and /var (thus /var/crash) that's big enough to
handle a kernel panic is important to me, so effectively the more RAM's
in the machine the bigger the SSD needs to be.  80GB seems to be okay
for our setups.

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