Re: Is EMC's CAS Centera considered "permanent data"?

In article <kujdp195lqoem59o72e8kpqjkpe18mf23k@xxxxxxx>,
HVB <devnull@xxxxxxxxx> wrote:
....
>The unspoken policy (not just from EMC) has always been to get disk
>customers to upgrade to the latest technology within 3 to 5 years of
>initial purchase. Usually this is achieved by making the maintenance
>costs higher than acquisition costs for the new equipment. However, I
>still know some people using 10 year old Symmetrix arrays because they
>dare not change anything.

This is not just unspoken policy. It is also
- sensible: Disks have a finite MTBF. If you care about your data,
you have to store it on redundant disks. And even redundancy can't
deal with frequent disk failures - because as soon as disks in a
redundancy group (for example in a mirror pair) fail, the group is
no longer redundant, until a spare disk can be brought into the
redundancy group. And with really old equipment, it is no longer
feasible to acquire spare disks that are compatible with the old
ones. Therefore you have to move your data to new disks (or in
general, to new media, which often implies to a next-generation
system).
- openly known: I doubt that any sales/marketing info coming from the
major vendors will make you believe that it is both technically
possible and economically viable to run your storage systems (disk
arrays) for very long times, for example in excess of 10 or 20
years. It is always possible that there are dishonest sales people
that might imply that, or even say it (without backing it up on
paper); I would even guess that not even my past, present and future
employers are immune from having at least a few dishonest sales
people. But as a rule, storage systems (both disk and tape) have
finite lifetimes, and everyone knows it.

With disk MTBFs traditionally having been around 100K hours (about 12
years), and the requirement that within a redundancy group no more
than 1 disk (with traditional RAID levels 1...5) fail at a time, an
expected lifetime of about 5 years for a storage system makes sense.
Massively increasing that requires either longer-life disks, or
regularly replacing the disks.

--
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Ralph Becker-Szendy _firstname_@xxxxxxxxxxxxxxxxxxxxxxxxxx
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