On 2010-09-07 22:47, Scott Marlowe wrote:
Ok, recently I have compared prices a NexSan SASBeast with 42 15K SAS
drives
with a HP MDS600 with 15K SAS drives.
The first is 8gbit Fibre Channel, the last is 3Gbit DAS SAS. The
fibre channel version is about 20% more expensive pr TB.
So of course it is a "fraction of the cost of a SAN", but it is a
fairly small one.
Are you really comparing equal systems? "8gbit Fibre Channel" means a
single Fibre Channel shared by 42 disks, whereas "3GBit DAS SAS" means 42
3gbit channels running in parallel. It seems like you'd really need some
realistic benchmarks that emulate your actual server load before you'd know
how these two systems compare.
Well, not usually. Most SAS DAS systems use a single multi-lane cable
that gives you 4x3GB channels, etc.
However, unless you're doing little than sequentially scanned reports
of a large size being read, the difference between 8gb and 3gb is not
going to matter. There are lots of very hard working transactional
databases that are lucky to see more than 20 or 40 megabytes a second
getting trasnferred spread out over 30 or 40 drives.
What really matters here is if the 8gb SAN is as fast as or faster
than the DAS setup. For most people measuring the speed of the
interface is a lot like the famous Tom Lane quote about benchmarking
jet fighters versus airliners by measuring the amount of runway they
need.
If you can get 10k tps on the SAN and 10k tps on the DAS
So to the OP, what are hoping to get from the SAN that you won't get
from the DAS? Also, how reliable are these two in comparison to each
other is kinda of important. Speed of the interface isn't a real big
deal for a database server Size of the battery backed cache in each
one is And how each survives the power plug pull test. If your SAN
salesman balks at a power on test you don't have to run it, you'll
know.
All wise words, that I can acknowledge with "hands on" experience.
I was basically only reacting to the "you can do the choice based
on cost alone.. DAS is soo-much-cheaper". In the comparison, I get
an equal amount of disks with same characteristica, in the same
raid-configuration. 1-2GB Battery backed cache on each. So on
paper, I think the systems are directly comparable. In the real
world it is more about "feelings" since I never get to benchmark both of
them.
Jesper
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Jesper
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