* why does df spin up disks?
@ 2015-06-29 1:43 Russell Coker
2015-06-29 7:13 ` Holger Hoffstätte
0 siblings, 1 reply; 2+ messages in thread
From: Russell Coker @ 2015-06-29 1:43 UTC (permalink / raw)
To: linux-btrfs
When I have a mounted filesystem why doesn't the kernel store the amount of
free space? Why does it need to spin up a disk that had been spun down?
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* Re: why does df spin up disks?
2015-06-29 1:43 why does df spin up disks? Russell Coker
@ 2015-06-29 7:13 ` Holger Hoffstätte
0 siblings, 0 replies; 2+ messages in thread
From: Holger Hoffstätte @ 2015-06-29 7:13 UTC (permalink / raw)
To: linux-btrfs
On 06/29/15 03:43, Russell Coker wrote:
> When I have a mounted filesystem why doesn't the kernel store the amount of
> free space? Why does it need to spin up a disk that had been spun down?
Most likely because the inode has been evicted due to memory pressure. I can df my mostly-idle backup disk "most" of the time without it spinning up once it has been mounted & gone to sleep (just did!), but if there's been significant memory movement (or issuing drop_caches) on the box it will spin up again sometimes. This is not unique to btrfs; other filesystems - at least ext4 - do this too, even though they might manage their expiry behaviour differently.
Now, whether the root inode and whatever is required for a df *should* ever expire after mounting or stay pinned, well..you'd have to ask the vfs folks.
-h
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2015-06-29 1:43 why does df spin up disks? Russell Coker
2015-06-29 7:13 ` Holger Hoffstätte
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