Well, 15,000 RPM works out to 250 RPS. However, I seriously doubt that
a RAID disk will read exactly 57K of emulated track per revolution.
Whether it is more or less, I haven't a clue.
(IBM Mainframe Discussion List) wrote:
In a message dated 2/8/2008 3:45:21 P.M. Central Standard Time,
[EMAIL PROTECTED] writes:
On FICON it would be reasonable to expect to get 50MB/sec to and from your
Disk and tape drives.
...
So 54,000MB at 50MB/sec is 1080 seconds, or 18 minutes.
I may be wrong, but I think backup/archive/retrieval/migrate products that
are operating on a whole volume level do each track serially, so a backup of a
really huge volume would be limited by the slowest part of the I/O path which
I believe will be the rotation speed of the disks. No matter how big the
controller's cache is, sooner or later a backup of an entire really huge volume
is going to slow down to match the track rotational speed. The SLED 3390
rotated at 70 RPS, which at 57K per track yielded about 4MB/second. RAID
disks rotate a lot faster than the 3390 did, but I think it's on the order of
twice the RPS rather than 10 to 20 times as fast. I would expect that a
controller could not cram more than 10MB per second into that 50MB FICON channel
unless the backup product is doing some kind of multitasking or similar
operation whereby it can do multiple large-scale reads at the same time. There's no
other way to break the rotation barrier. Do backup products work like that
yet? 54000 MB at 10MB/second = 5400 seconds = 90 minutes.
Bill Fairchild
Rocket Software
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