Discussion:
Z13 dasd support
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Peter
2017-10-02 03:08:08 UTC
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Hi

Is there any constraint for the z13 to support any maximum number of
storage device attached to it ? I mean precisely how many online Dasd it
can support at one time and is there factors involved here ?

General query to understand the capability of z13.

Regards
Peter

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R.S.
2017-10-02 08:24:04 UTC
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Post by Peter
Hi
Is there any constraint for the z13 to support any maximum number of
storage device attached to it ? I mean precisely how many online Dasd it
can support at one time and is there factors involved here ?
General query to understand the capability of z13.
There is no simple number.
Some remarks:
1. A storage device can be understood as DASD box (HDS, IBM, EMC), or as
a (emulated) device attached to the OS. Let's focus on the second
definition.
2. Single OS (operating system - like z/OS) can have up to almost 64k
devices. Plus aliases, plus PPRC secondary. That's the simplest answer.
3. The above limitation is not for OS, not for LPAR, it's for CSS. z13
(big one) has 6 Channel Subsystems, so one can have up to 6x(64k-256)
devices plus aliases plus PPRC secondaries. Minus othe devices like
consoles or tape drives.
4. A device can be up to 1TB big.

HTH
--
Radoslaw Skorupka
Lodz, Poland




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John Eells
2017-10-02 12:47:56 UTC
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Post by Peter
Hi
Is there any constraint for the z13 to support any maximum number of
storage device attached to it ? I mean precisely how many online Dasd it
can support at one time and is there factors involved here ?
General query to understand the capability of z13.
Thre are two answers to this question. The first is a z/OS answer. You
may attach up to 65,280 devices and address them directly (that is,
define them using subchannel set zero). Subtract from this number how
many device numbers you consume for other things (consoles, tape,
networking, etc.). You can also access some volumes for IPL processing
using a nonzero subchannel set. Additionally, devices used for certain
things (such as replication) can be attached using other subchannel
sets, which acts as a multiplier for the total.

The second is a hardware question. How many FICON channels can you
attach to a z13, how many disk control units can you attach to each, and
how many volumes can be defined for each disk control unit? I do not
know the answers to these questions but they should not be difficult to
find if you look. Without having looked, though, I am confident that
the hardware supports more attached devices than the software will
support in subchannel set zero, and pretty sure it will support
considerably more than that.

In practical terms, the answer is pretty close to "however many you
want," but it is possible to define small or small-ish device sizes and
hit the limit. With EAVs, though, you can have a *lot* of online,
spinning data, and I don't know of anyone who has yet hit that limit.
--
John Eells
IBM Poughkeepsie
***@us.ibm.com

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