Fusion Drive - Determining How Much Each is Filled

p3ntyne

macrumors 6502
Original poster
Jan 10, 2014
406
3
Sydney, Australia
Hi,

I have just loaded lots of data onto my fusion drive and I am wondering if there is any way to know how full each drive is.

Thank you.
 

Weaselboy

Moderator
Staff member
Jan 23, 2005
29,403
8,989
California
Not really... the system sees the Fusion as one drive. In theory though, the flash portion would always be almost full as the system tries to move the most frequently used data to that device.

Give this article a read. You can sort of deduce where data is stored by watching disk activity using iostat while you copy files around.
 

Tumbleweed666

macrumors 68000
Mar 20, 2009
1,651
47
Near London, UK.
As per Weaselboy, the flash portion should always be full or nearly so, but what its full with will change, so there is no point knowing what with, and the only thing that will change is how full the hard disk part is as you gain or remove data.
 

blevins321

macrumors 68030
Dec 24, 2010
2,758
70
Winnipeg, MB
I believe that you can do Applications>Utilities>Terminal.

Try the following two commands:

diskutil list

diskutil CoreStorage list

It will tell the actual used space for each partition. Can't remember if the first one will give the individual components for a fusion drive or not.
 

gnasher729

macrumors P6
Nov 25, 2005
17,178
3,134
Hi,

I have just loaded lots of data onto my fusion drive and I am wondering if there is any way to know how full each drive is.

Thank you.
The OS tries to have the SSD drive full except for 4 GB that are used as a write cache. When you write data the write cache is filled; when you stop writing the OS empties the write cache so that the SSD drive has 4 GB free again. If you delete data that happens to be on the SSD drive, then the OS fills it up again with data from the hard drive when you stop using the drive for a second.
 

Weaselboy

Moderator
Staff member
Jan 23, 2005
29,403
8,989
California
I believe that you can do Applications>Utilities>Terminal.

Try the following two commands:

diskutil list

diskutil CoreStorage list

It will tell the actual used space for each partition. Can't remember if the first one will give the individual components for a fusion drive or not.
That will show the total space used by the Fusion logical volume, but it does not break it down by the individual, physical disks. It will just show the size of each physical disk, but not space free/used.