Storage capacity

[Mattt]

Hi,

I understand that the spec doesn't provide a mechanism to retrieve the
storage capacity (i.e. free space) of the underlying storage system.
Which means that each VIM could(!) use the XAM-extention API to
provide such information in "vendor specific" fields.
IMHO this contradicts the XAM-idea as I have to modify my application
for each storage subsystem I want to support -- instead of having a
generic interface for all VIMs.

Ok, for some systems it might be difficult to calculate/report their
storage capacity (e.g. tape libraries), but the IBM Tivoli SSAM shows
a valid approch by using a virtual container (aka file space) that is
being set to a certain size. (The administrator then has to make sure
that enough storage hardware available.)

Am I missing something, or is this a valid point?
Matthias

[Mark]

It's a valid thing to want to do for managing XSystems, but not
necessarily
through the XAM Interface. It was thought that the type of application
that
would want to manage Capacity and other aspects of the storage itself
would
be an SRM or SAN Manager using the SMI-S interface.

The SNIA FCAS TWG is looking into an SMI-S profile definition for
XSystems
that could be independent from any given release of the XAM interface.

-- mark

[Mattt]

Our application as well as any software that wants to put data onto
storage needs to know how much space is left. Well, it makes life alot
easier. Usually it's better to display a warning "unsufficient space"
*before* the write attempt, instead of "no space left on device" after
an unsuccessful (but time consuming) write call.

That being said and the fact that most storage vendors will/do make
this information available through additional fields makes it a valid
request for non-managing applications as well. I surely do not want to
manage, I want to use. And it better I know how much I can use.

Matthias

[Michael Matthews]

I'm new to the archiving world so this may be an ignorant question,
but are you assuming a single application talking to the storage
system? Asking up front for capacity will work in that case but if
you have multiple applications sharing a single storage system then
you can check available space but it may fill up before you can
complete the store anyways.

Is that the typical scenario in the archiving world? Is the storage
system typically shared among applications or not?

Thanks,
Michael

[Mattt]

No, this is a valid scenario. And I do not persist in an exact byte
count (that could change every second), but I need a "hint" about the
free capacity (like: "Is it worth to try?".
It's always possible that another application puts data on the storage
system and also that hardware failures reduce the available capacity.
I still would have to capture potential write errors because the
system is running out of space.

As I said, it makes life alot easier if this information is available
(being exact or not). The funny thing is that the information *is*
available in the underlying layers. It just that XAM doesn't provide
access to it. To me this sounds like a bug :)

Matthias

[Mark]

Matt,

Didn't mean to imply this was not a valid request. After all,
filesystems have
a "df" command for applications to use. I will send a note to the FCAS
TWG
to add this to the list of requirements for XAM 1.1.

Is there functionality you require beyond the equivalent of "df"?

-- mark

[Fineberg, Sam]

In a some systems the amount of free space can be complicated (i.e., is all the space available for one stream or not, does de-dup or compression affect available space, do you need temporary space, etc.). The best approach would be to pre-allocate your storage, or if your system supports it, to hint the stream size.

Sam

----------
Samuel A. Fineberg, Ph.D.
Distinguished Technologist/Technical Strategist
Information Management Chief Technologist Office
Business Information Optimization, HP Software
19111 Pruneridge Ave., MS 4086; Cupertino, CA 95014
fine...@hp.com
Phone: +1-408-447-3776, Mobile: +1-650-283-0338