On 2/5/2011 5:44 AM, Orvar Korvar wrote:
So... Sun's SSD used for ZIL and L2ARC does not use TRIM, so how big a problem
is lack of TRIM in ZFS really? It should not hinder anyone to run without TRIM?
I didnt really understand the answer on this question. Because Sun's SSD does
not use TRIM - and it is not consider a hinder? A home user could use SSD
without greater problems? If I format the disk every year and reinstall, would
that help? I am concerned as a home user...
As a home user, you don't really care about support for TRIM. Even a
reasonable SSD (i.e. not "Enterprise" level) will provide a very
significant boost when used as a ZIL, over just having bare drives (in
particular, if you just have SATA 7200 or 5400 RPM drives, you will
really notice the boost). Ideally, you want an SSD with a battery or
supercapacitor, but they're pretty expensive right now. (i.e. OCZ's
Vertex 2 Pro series).
If you have a dependable UPS for the system, and can accept the (small)
risk that you might lose the last write commit on certain power-loss
scenarios, a mid-line SSD is entirely OK.
Note that a ZIL cache device is NOT A WRITE CACHE. ZIL is there for
synchronous writes only, so that ZFS can essentially turn synchronous
writes into asynchronous writes. NFS is a big sync() write user, but
Samba is not. You won't notice any improvement over Samba when using a
ZIL cache.
Don't bother with a reformat of the SSD. It won't help, other than maybe
a yearly reformat would be good to reset absolutely everything inside
it, but, you won't notice any really difference even after you do.
Regarding the DDRAM SSDs that dont need TRIM, they seem interesting. I got a
mail from CTO of DDrive who did not want to mail publicly to this list
(advertisment he said) but it seems expensive, the DDdrive X1 which is targeted
to Enterprise costs $2000 USD. Are there any home user variants? But reading
this presentation, it seems to have a point of using DDRAM variants:
http://www.ddrdrive.com/zil_accelerator.pdf
Quite interesting info
There are a couple of things similar to the DDRdrive, but they're all
Enterprise-class, and going to cost you. There's no $200 solution.
Which is kind of sad, since building a DDRdrive-like thing reallly just
requires 2 4Gbit DRAM chips, 2 4GBit NAND chips, a small battery, and a
FPGA that does some basic PCI-E to Memory mapping (and, a little bit of
extra DRAM->NAND copying if power is lost). Really, it's entirely
doable for someone with decent VLSI experience. The DDRdrive folks have
got the experience to do it, but, honestly, its not a complex product.
Bottom line, it's maybe $50 in parts, plus a $100k VLSI Engineer to do
the design. <wink>
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
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