User talk:Guy Harris/Archives/2016/07

Some SNIA definitions

Hello! Regarding edit here. I have noticed that one article was missing, but had to review my history to spot it :)

First off, "secondary" is not used by my source, so "the SNIA dictionary's discussion of partitioning discusses dividing *secondary* memory" is not correct or not correctly phrased. Another note that Memory management (operating systems) starts with "In operating systems, memory management"... "for managing the computer's primary memory" but then in section Memory_management_(operating_systems)#Partitioned_allocation it uses only "primary memory... usually contiguous areas of memory"

It is untrue that "memory" means "primary memory" (see Memory hierarchy).

How can we improve definitions? I don't want to split Memory_management_(operating_systems) because of 1-2 terms. Ushkin N (talk) 07:56, 30 July 2016 (UTC)

It is, however, 100% true that memory management is discussing primary memory - it says so quite explicitly.

Furthermore, what the SNIA dictionary says about "partition" and "partitioning" is:

partition

1. [Storage System] A subdivision of the capacity of a physical or virtual disk.

2. [Storage System] A contiguously addressed range of logical blocks on a physical media that is identifiable by an operating system.

Partitions are consecutively numbered ranges of blocks that are created and used by MS-DOS, Windows, and most UNIX operating systems.

partitioning

[Storage System] Presentation of the usable storage capacity of a disk or array to an operating environment in the form of several virtual disks whose aggregate capacity approximates that of the underlying physical or virtual disk.

Partitioning is common in MS-DOS, Windows, and UNIX environments. Partitioning is useful with hosts that cannot support the full capacity of a large disk or array as one device. It can also be useful administratively, for example, to create hard subdivisions of a large virtual disk.

which explicitly speaks of disks or arrays (meaning arrays of disks), except for definition 2 of "partition", which just implicitly speaks of disks or arrays of same. (Perhaps they should update it to speak of flash memory and other non-disk non-volatile storage technologies as well.)

Given that primary memory is "is the only [form of data storage] directly accessible to the CPU", that means disks aren't primary memory on modern computers (I guess one could build a machine that uses disks as primary memory, just as machines were built that used drum memory as primary memory, but nobody's building machines like that - all the CPU can do is tell the disk controller "fetch this block into this location in primary memory" or "write to this block from this location in primary memory".

So the SNIA dictionary isn't talking about primary memory; given that "secondary storage", in both the computer data storage article and the auxiliary memory, includes disk storage, what it's talking about is secondary memory, even if they don't use that term.

HTH. Guy Harris (talk) 08:36, 30 July 2016 (UTC)

Thank you for formatting definitions, so we can discuss them here in detail.

It very clearly states "or virtual disk", please don't read only part that about "arrays" (yes, it's about ordinary arrays/RAID).

Again, SNIA, never limits itself to "array"/"only RAID". Authors are well aware about Storage virtualization nuances.

From my professional experience, I can tell that any "file only" system can be stored in main memory using RAM disk.

Similarly, it is possible to store "main memory" in SAN simply by moving "swap" file to SAN. You never do this in operational phase, but it can be the case in backups/virtualization.

They talk about quite abstract memory, not really about "secondary"; otherwise you would provide direct quote from SNIA.

I researched SNIA terminology for some time, and they really not using 1/2/3/4 level of memory separation, as we do at Wikipedia.

I would like to see statements about "secondary" or "primary" from SNIA, otherwise my statement still holds, just my 2c. Ushkin N (talk) 18:07, 30 July 2016 (UTC)

According to this obscure document called the "SNIA dictionary", a "virtual disk" is

[Storage System] A set of disk blocks presented to an operating environment as a range of consecutively numbered logical blocks with disk-like storage and I/O semantics.

The virtual disk is the disk array object that most closely resembles a physical disk from the operating environment's viewpoint. See logical disk.

so a "virtual disk" has nothing to do with primary memory. Guy Harris (talk) 18:18, 30 July 2016 (UTC)

But actually, I'm looking at Disk partitioning and this page may be sufficient in Category:Computer storage terminology; but it wasn't clear from your edit message tho. Ushkin N (talk) 08:10, 30 July 2016 (UTC)

Let's not discuss popularity of something. Personally I find their terminology as incomplete compared to Wikipedia but very practical and short on another hard.

SAN, presented as "block storage" with I/O semantic will qualify as "virtual disk".

RAM disk presented as "block storage" with I/O semantic will qualify as "virtual disk".

And thank you for the quote, there no "secondary storage" or "secondary memory" words; your claim "nothing to do with primary memory" is really unsourced/WP:OR. Ushkin N (talk) 18:52, 30 July 2016 (UTC)

For example, it ignores NAS/DAS distinction.

"closely resembles a physical disk from the operating environment's viewpoint" is the most important part of the definition IMO

Virtual disk is an abstraction of the really complex hardware behind to what is posed as "virtual disk".

Operating system shouldn't care if it was a local raid array or remote raid array or it was NAS or something more complex.

If it can put files on it (block addressing, same IO system callbacks), it's a disk. Ushkin N (talk) 19:16, 30 July 2016 (UTC)

Yes, the words "partition" and "partitioning" are used in several different contexts in computing; see, in addition to memory management (operating systems) and disk partitioning, network partition, for example. The type of partitioning to which the SNIA is referring is disk partitioning, which is different from the partitioned memory allocation discussed in memory management (operating systems). Guy Harris (talk) 09:05, 30 July 2016 (UTC)

Again, there no statements about "disk partitioning" in SNIA, they use general term "partitioning" and other (memory) related terms.

Yes we have everything spitted in Wikipedia, but not everyone makes distinction between primary memory partitioning and secondary memory partitioning. Ushkin N (talk) 18:07, 30 July 2016 (UTC)

They don't say "disk" because, given that this is the SNIA, it should be clear to all that they are speaking of equipment with disk-like semantics, even if they happen to be made of, for example, flash memory. Guy Harris (talk) 18:18, 30 July 2016 (UTC)

Plesae open http://www.snia.org/ it has "cloud storage" and "linear tape system" and "Ethernet storage" thing.

They are not focused only on hard drive disks. At least not all of them, or not today. Ushkin N (talk) 18:52, 30 July 2016 (UTC)