From: Erik Trimble [mailto:erik.trim...@oracle.com]
Sent: 星期一, 五月 24, 2010 16:28
To: Fred Liu
Cc: ZFS Discussions
Subject: Re: [zfs-discuss] [ZIL device brainstorm] intel x25-M G2 has ram cache?
On 5/23/2010 11:30 PM, Fred Liu wrote:
Hi,
I have hit the synchronous NFS writing wall just like many people do.
There also have lots of discussion about the solutions here.
I want to post all of my exploring fighting done recently to discuss and share:
1): using the normal SATA-SSDs(intel/ocz) as ZIL device. For intel just EOLed
50nm SSDs product line and the spec of the x25-M G2(34nm) 160G is getting
more decent, I used this one. I get good performance boost compared with
no slog.
I also manually did unplugging power server times, the outcome seems good
-- I got
no data corruption. But there is always potential risk �C does it have
built-in ram cache?
We get no clear answer from intel.
yes, both the X25-M (both G1 and G2) plus the X25-E have a DRAM buffer on the
controller, and neither has a supercapacitor (or other battery) to back it up,
so there is the potential for data loss (but /not/ data corruption) in a
power-loss scenario.
Sadly, we're pretty much at the point where no current retail-available SSD has
battery backup for it's on-controller DRAM cache (and, they /all/ use DRAM
caches).
[Fred]: Yes. It is correct. I totally agree.
2): using PCIE-SSD(i.e. fusionio’s ioDrive). For the universal standard of
PCIE-SSD is still on the way, the responding driver
under solaris become apparent. And also the cost is very high.
Yes, you do have to find those with Solaris drivers. Fortunately, pretty much
all the manufacturers recognize the big market that ZFS/Solaris has for these
devices, so most already have Solaris drivers, and the rest are almost
universally working to produce them.
[Fred]: Yes. Hope we can see the very first standard soon just like USB…
3): using PCIE-DRAM-with(out)-SSD(i.e. marvell’s write acceleration module
(WAM), ddrdrive X1, curtisssd’s
HyperCache. It has the higest spec but the same driver and high cost issue.
Yup.
4): using SATA--DRAM-with(out)-SSD(i.e acard’s 9010, curtisssd’s HyperHD). No
driver issue and price is in the middle.
I also tried acard 9010, the result is good enough.
Frankly, these are about the best available solution, without breaking the
bank. The bad news is that they're not quite read-for-prime-time yet in terms
of support and packaging.
[Fred]: Agree.
So it seems we have to wait awhile to get a really ideal ZIL device solution.
If intel/ocz can confirm no ram cache, that will be good news.
Thanks.
Fred
Nope, ALL SSDs use DRAM caches for their controllers. So far, I'm only aware
that the Zeus stuff (plus a couple of industrial/military-only products) have
battery backup for their controllers. Idiots - it's like $0.50 in parts, and a
one-time $10,000 in engineer design/qa time to put the damned thing on, and
they could charge a 25% premium and we'd pay it.
Frankly, I'm really surprised that there's no solution, given that the *amount*
of NVRAM needed for ZIL (or similar usage) is really quite small. a dozen GB is
more than sufficient, and really, most systems do fine with just a couple of GB
(3-4 or so). Producing a small, DRAM-based device in a 3.5" HD form-factor
with built-in battery shouldn't be hard, and I'm kinda flabberghasted nobody is
doing it. Well, at least in the sub-$1000 category. I mean, it's 2 SODIMMs, a
AAA-NiCad battery, a PCI-E->DDR2 memory controller, a PCI-E to SATA6Gbps
controller, and that's it.
[Fred]: Agree. I am struggling so hard to procure that kind of device, but it
is so hard to find for an individual.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
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