Cross-posting this to freebsd-fs, as I'm sure people there will have
other recommendations. (This is one of those rare cross-posting
situations.....)
On Fri, Oct 31, 2008 at 01:14:55PM +1000, Danny Carroll wrote:
I think these sets of tests are good. There are some others I'd like to
see, but they'd only be applicable if the 1231-ML has hardware cache. I
can mention what those are if the card does have hardware caching.
The general concept is: "the more RAM the better". However, if you're
using RELENG_7, then there's not much point (speaking solely about ZFS)
to getting more than maybe 3 or 4GB; you're still limited to a 2GB kmap
maximum.
Regarding size of the array vs. memory usage: as long as you tune kmem
and ZFS ARC, you shouldn't have much trouble. There have been some
key people reporting lately that they run very large ZFS arrays without
issue, with proper tuning.
Also, just a reminder: do not pick a value of 2048M for kmem_size or
kmem_size_max; the machine won't boot/work. You shouldn't go above
something like 1536M, although some have tuned slightly above that
with success. (You need to remember that there is more to kernel
memory allocation than just this, so you don't want to exhaust it all
assigning it to kmap. Hope that makes sense...)
Only on CURRENT; 7.x cannot, and AFAIK, will never be able to, as the
engineering efforts required to fix it are too great.
I look forward to seeing your numbers. Someone here might be able to
compile them into some graphs and other whatnots to make things easier
for future readers.
Thanks for doing all of this!
--
| 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 |
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