Penang said:
Please pardon me if this topic has been discussed before, but as far
as I know about the Flash memory, they have a relatively low limit on
re-write, as compared to hard disk
In situation where database use in concern, read and write operation
takes place very often
I know that there are pros and cons in this issue, but basically my
question is this --- How reliable is SSD?
http://www.imation.com/PageFiles/83/SSD-Reliability-Lifetime-White-Paper.pdf
The last page of the report addresses "wearout" as a function of writes.
As far as I can tell, they use the best kinds of writes (large sequential),
to make the estimate.
The flash block size is 128KB. If you want to update 4KB of that,
you have to rewrite the whole thing. So relatively speaking, it is
"32x" more expensive, to deal with the small sized write.
To understand whether SSD may be of value to you, you need to know
how much data you write per day. If it is a small amount, then it may
not matter what size the writes are. If you write large amounts of
data, then you'd want to understand the characteristics very well.
(That means sorting all the writes into "size bins".)
Before you buy anything, you should also read some recent reviews
of SSD products, and some of the performance problems they can have.
Don't just buy the SSD with the lowest price. You're regret it.
This is a hint as to what you're looking for. There are more articles
around, which test for this.
http://www.anandtech.com/cpuchipsets/intel/showdoc.aspx?i=3403&p=8
If you want to build a test system for evaluation, use Intel
X25-E SSDs.
*******
None of the above addresses "reliability" as such. The above addresses
"wearout", where you know the thing will eventually fail, as a function
of how many writes you've done. Wear leveling makes the most of the
write cycle limits of SLC or MLC flash chips.
Reliability takes into account other things, like how often a
flash chip just rolls over and dies for no particularly good reason.
Take the stick of RAM in my previous computer as an example - one entire
chip stopped responding, after about two years of usage. Why did that happen ?
That is an example of something not accounted for as wearout -
that is a device failure unrelated to usage. RAM should not
wear out. And yet I've had failures at the two year mark (the
stick was not abused, and the computer case is cooled well).
If the chips in a flash drive do that too, then not only would
I have wearout to consider, I'd have device reliability
(chips dying) to add to the effect. And the only way to study that
in any effective way, is to get field return data for SSD drives.
And nobody gives out field return data.
Paul
