"Size on disk" means what? OneDrive clarification

Kari · 14 Jul 2019

Difference between actual size and size on disk has nothing to do with compression.

Default Allocation Unit (AU) size on an NTFS formatted disk is 4 Kb (4,096 bytes):

"Size on disk" means what? OneDrive clarification-image.png

One AU can only contain data from one file. Any unused space in an AU will be lost, it can't be used to store data from another file. A file from 1 up to 4,096 bytes uses one AU, a 4,097 bytes file requires two AUs, and so on.

Theoretically, if a data disk is only used to store small files, you could save some disk space by selecting a smaller AU size when formatting. In reality, the possible disk space saved would be meaningless, thinking of todays SSD and HDD sizes.

If your data drive is used only for extremely large files like for instance HD TV shows and movies, you might gain a little better performance using larger AUs, because Windows would need to go through less AUs when you play the movie. But, again, the difference would be practically unnoticeable.

An example. In screenshot properties of a small Word document:

The file is 22,692 bytes. On disk, it requires 6 AUs (6 * 4,096 = 24,576 / 24 Kb) because it is 2,212 bytes too big to fit in 5 AUs (5 * 4,096 = 20,480). In other words, this last 2,212 bytes of the file is stored on last AU. The rest of this AU (1,884 bytes unused space) cannot be used to store data from any other file, file system marking the whole AU reserved.

Kari

clayto · 16 Jul 2019

Thanks for the technical detail. I am not sure how it relates to my issue, which is basically that I have been unable to reduce the amount of space taken by One Drive. I t remains at Size 16.7 GB, Allocated 14.9 GB, whereas I think it should be closer to zero. I have just spent several hours manually making files 'Online only' and in some cases 'Keep online' without it having any effect on the space consumed. Have I done the right thing? What is the difference between 'Online only' and Keep online' if there is one? I presume I am correct in assuming that 'online only' means not on my computer (though available from it.)?

Having now only 5 GB free after 7 GB disappeared I want to get this sorted out, before attempting the current update (though I understand it can still be done --- as before --- with the help of an external drive.)

clayto · 16 Jul 2019

Further to my post above about my One Drive not having space saving (and other) options in Settings the snip below shows the only Settings which are displayed in my One Drive app

mngerhold · 16 Jul 2019

I do not know for sure, but it is entirely possible (and reasonable) that the 'online' settings won't remove a file already on your local system. So try Wiztree to confirm what is actually on your local drive, then (as long as the files are known to be online, and preferably backed up somewhere else), try removing the local copies.

clayto · 16 Jul 2019

I think I may have found the, or at least one, cause of the problems. I do not have, and suspect I never have had, the OneDrive Action Centre with is access to settings / options on my OS. It may be that it was missed out of the update that introduced it a while back, or is present but not enabled. I see there is a way to enable it using a reg edit. This is something I generally avoid as it is not something I am confident to do. I am awaiting a response from MS Support.

clayto · 16 Jul 2019

That should read Activity Centre not Action Centre. It seems this might be solved by RESETTING or UNINSTALLING OneDrive. I need to be sure that neither of these will wipe out what I have installed in OneDrive. I am not sure whether there is a risk with this as what is stated seems unclear and contradictory.

Kari · 16 Jul 2019

clayto said:

Thanks for the technical detail. I am not sure how it relates to my issue.

I am sorry if you did not understand my reply, sorry that I answered your question. You asked a specific question "Size on disk" means what?" in your thread title. I answered that exact question, and you were unhappy with my answer. It's like asking what's 10 times 10, and when someone answers it's 100, you would say that you did not want to know how much is 10 times 10.

Next time, I try to remember that when you ask something, you do not want an answer to that question.

OneDrive Files on Demand feature works. If you have any issues with it, see the tutorial: Turn On or Off OneDrive Files On-Demand in Windows 10

You can turn it on or off as you wish:

Kari

clayto · 19 Jul 2019

Thanks for displaying the menu above (Settings etc) because it has confirmed what may be the core of the problems, which is that I do not have that menu on my system! It is the first time I have seen it, and I have not discovered any way to bring it up despite repeatedly clicking everything in sight. I am sure now that OneDrive on my PC is corrupt or at least partly missing, or perhaps there are features present but not enabled. As a result I am now in correspondence with a Support tech from a dedicated OneDrive service and hopeful that we will soon have it working correctly..

Dave Carter · 28 Nov 2019

Kari said:

Difference between actual size and size on disk has nothing to do with compression.

Did you not even read the other posts? He said the size on disk was smaller than the size of file, and others went into it, speaking about compression, to post incorrectly while ignoring others is not helpful.

The size on disk was smaller due to COMPRESSION, NTFS Compression. Its under the ADVANCED button on the properties box use showed.
From memory it takes 64K blocks of the file compresses them using LZW and if that fits onto less AU than raw 64K does then it is written as a compressed fragment, this allows for dynamic access without having to decompress the whole file including the ability to write sections of the file without full re-compress.

The size on disk when in the off disk in the OneDrive cloud is zero, this is represented on disk is an untouched NTFS SPARSE file. OneDrive then intercepts reads to sparse files and downloads them as a raw file then passes control back to the OS to read the file.

On reading the whole thread the OP wants to know why if he is saving space by compressing his disk then why it used more space, and the cause is he wasn't saving space, he was converting files from a OneDrive NTFS SPARSE (no space used) file to a NTFS COMPRESSION file, so they were download and compressed.

Unfortunately he cant even now store them offline and expect them to download to disk and store compressed even if the folder is set to that as OneDrive is side stepping the OS NTFS compression control and deliberately storing the file uncompressed, this is likely to minimize out of disk space events on files that content modified that then require more space when on the physical disk due to the new content not compressing as well.
(this behavior of OneDrive was what brought me to this thread by the way, as it is an undocumented action of OneDrive that violates the intention of the NTFS compression control on the file system, Microsoft have been cagey in there replies to me so far on this subject, I suspect it is enforced in preparation for delta syncing to be added to OneDrive and they simply felt compression was no overly used so lets ignore it)

Pluginz · 28 Nov 2019

Goto 'Control Panel, then 'System'. Then Advanced Tab At bottom you will see Environment Variables.
In there should be your One Drive account and location. If not then problems will occur. Good luck chap