From: "Holger Hoffstätte" <holger.hoffstaette@googlemail.com>
To: linux-btrfs@vger.kernel.org
Subject: Re: why does df spin up disks?
Date: Mon, 29 Jun 2015 09:13:06 +0200 [thread overview]
Message-ID: <5590F002.1040209@googlemail.com> (raw)
In-Reply-To: <201506291143.59911.russell@coker.com.au>
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
prev parent reply other threads:[~2015-06-29 7:20 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-29 1:43 why does df spin up disks? Russell Coker
2015-06-29 7:13 ` Holger Hoffstätte [this message]
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