Messages in this thread | | | Date | Fri, 07 Dec 2012 16:49:04 -0500 | From | Ric Wheeler <> | Subject | Re: [PATCH, 3.7-rc7, RESEND] fs: revert commit bbdd6808 to fallocate UAPI |
| |
On 12/07/2012 04:43 PM, Chris Mason wrote: > On Fri, Dec 07, 2012 at 02:27:43PM -0700, Theodore Ts'o wrote: >> On Fri, Dec 07, 2012 at 04:09:32PM -0500, Chris Mason wrote: >>> Persistent trim is what I had in mind, but there are other ideas that do >>> imply a change in behavior as well. Can we safely assume this feature >>> won't matter on spinning media? New features like persistent >>> trim do make it much easier to solve securely, and using a bit for it >>> means we can toss back an error to the app if the underlying storage >>> isn't safe. >> We originally implemented no hide stale for spinning media. Some >> folks have claimed that for XFS their superior technology means that >> no hide stale doesn't buy them anything for HDD's. I'm not entirely >> sure I buy this, since if you need to update metadata, it means at >> least one extra seek for each random write into 4k preallocated space, >> and 7200 RPM disks only have about 200 seeks per second. > True, 7200 RPM disks are slow, but even allowing them to expose stale > data just makes them a little less slow. > > I know it's against the rules to pretend that disks don't matter. But > really, once you're doing random IO into a spindle you've given up on > performance anyway. > > -chris
That's right.
And equally true, once you have moved the disk heads to that track, you can write a lot as cheaply as a little (i.e., do 1MB instead of 4KB). That will also avoid fragmentation of the extents.
I think it would be good to see how much that gets back for us,
Ric
| |