Using an SSD "disk" for /

[Oliver Fromme]

Jeremy Chadwick wrote:
 > On Thu, Nov 04, 2010 at 03:29:22PM +0100, Oliver Fromme wrote:
 > > What kind of tuning do you apply to those file systems?
 > > 
 > > I'm asking because I can't really reproduce those results.
 > > On a machine with plenty of RAM I've created memory disks
 > > for obj and src, which should at least be as fast (probably
 > > even faster) than an SSD.  Buildworld was somewhat faster,
 > > compared to standard (well-tuned) UFS+SU filesystems on a
 > > fast SATA HDD, but not _that_ much faster.  In fact the
 > > difference was small enough that I stopped using memory
 > > disks and returned to using UFS+SU+noatime (and a few other
 > > tuning options) on a HDD.
 > > 
 > > So, if you experience a _dramatic_ speed-up when using SSDs
 > > for buildworld, I would really very much like to know why
 > > this is the case, and what kind of tuning you performed.
 > 
 > Literally: absolutely no tuning.  I treat the SSD the exact same as I
 > would a standard mechanical HDD: install FreeBSD on it, and that's that.
 > 
 > I imagine the performance difference greatly depends on what SSD you're
 > actually using.  Again, the Intel drives have the highest IOPS out there
 > (at least in the consumer-grade market), and I can't justify the cost of
 > an SLC-based drive, so I stick to MLC.
 > 
 > Possibly you and I have different interpretation of what "dramatic"
 > means?  :-)  My opinion is that cutting 6-7 full minutes off a
 > buildworld is pretty dramatic.

Well, here are some hard numbers:

With /usr/src and /usr/obj both on the same SATA-300 HDD,
a buildworld takes 10 minutes and 13 seconds.

With /usr/src and /usr/obj on separate memory disks,
a buildworld takes 10 minutes and 4 seconds.

This is stable/8 with empty /etc/src.conf, i.e. a complete
buildworld.  The machine is an AMD Phenom II X6 (hexacore).

I think 10:13 vs. 10:04 is not "dramatic".  I don't think
there's a way I can cut 6-7 minutes from that with current
(and affordable) hardware.

Best regards
   Oliver

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