Previously lars wrote:
Arno Wagner wrote:
RAID for memory? Are you sure you are not talking about ECC,
which is far better for memory? I do not expect this type of really,
really bad engineering out of IBM, unless the customer demands
it (due to incompetence). Care to list a reference?
YES sure!
Go to www.ibm.com do a search for "memory mirrored" you will among other
things find xSeries models and tech papers on this.
http://researchweb.watson.ibm.com/jo.../tremaine.html
and many many other.
Ok, that is for very high availability stuff only. And it is
not RAID in thst strict sense. It is mirrored memory that can
continue to operate through ECC failure. Unless the controller
and bus system is orders of magnitude more reliable than the
memory used, this makes no sense at al technologicaly.
And come to think of it there is still the problem of FRU if doing the
redundancy in the SSD itself. So for real life in a sever, no sir RAID
still has its advances - otherwise 24x7 can't be done.
RAID is fine. But RAID for SSDs is just a sign that the technology
is not being understood. The problem here is that while HDDs
a) typically fail as a unit and b) typically notice when they are
failing, RAID makes a lot of sense with HDDs. SSDs are more likely
to fail in memory locations. A quality SSD can compensate with ECC.
If it cannot, then its controller chip is shot )or something very, very
unlikely happened) and it may give arbitrary wrong data to the
user. RAID does not help at all in this case. Of course this is
simplified.
Arno
Still won't do in real life, SSD simply can't be sold as a "never failing
single device". There is no market in highend IT for such a thing!
A solution with the possibility of handling the SSD as a FRU is what it
takes - without question.
I never vclaimed that. But I expect a SSD is as reliable as the
disk controller in the first place and reduyndancy by multiple
SSDs makes no sense.
Not that I like refering to specific products, but this company I think is
close me my own thinking and the use of SSD's.
http://www.bitmicro.com/solutions_apps_comp_raidsys.php
Now...
Please take a good cup of coffee, and sit down for a while.
Having great new technology coming to market, is well... great :-)
But if 24x7 handling can't be given, then the new technology will have no
place in high end solutions. Solution keeps running while having failed
part replaced is what defines highend storage today - I think.
See above.
SSD will be banned to live its hole life in laptops etc.
And "never failing single device" well not good enough for highend storage
solutions..
So even if you are right SSD "technology is not being understood", you have
to understand the storage market better I think.
Not at all. I am not in the business of ripping customers off. I am a
customer that is an expert at the same time. As with the memory,
redundancy by having multiple SSDs only makes sense if the RAID
controller used is orders of magnitude more reliable than the SSD. I
doubt that is the case for typical SSDs and controllers. For HDDs it
is routinely the case.
So to put it as clear as I can, even if you beeing right today about
SSD it will take years (decades) before you could sell such stuff to
highend without extra security.
a) It is "safety" or "redundancy", not "security".
b) People buy all kinds of stupid stuff, because they do not understand
science and/or engineering.
c) A pair of high-reliability SSDs,
together with a high reliability RAID-1 controller is actually
less reliable than using one of the SSDs directly, if we assume
that a simple non-RAID controller is a lot more reliable. Do the
math. The assumption has merit, because the RAID-1 controller is
much more complex than a simple controller.
Arno