On Mon, Feb 17, 2014 at 10:44:47PM -0500, Martin K. Petersen wrote: > > Well, that has changed a bit with the logical block provisioning bits in > SCSI. That's why I brought up the allocation/deallocation assumptions in > the existing two blkdev_issue_foo() calls. Is it a fair assumption that the reason why T10 added these bits is mainly so that clients of thin-provisioned storage devices can guarantee that a subseq uent write won't fail? Since historically the spec writers have washed their hands of anything that might vaguely smell of performance considerations.... > Yeah. So deprovision with guaranteed zero on read is what you're > after. I'll chew on that a bit tomorrow. Yes. And also some way for the host OS (or some other underlying storage device, more generally) to send hints to the guest OS about the best way to tune filesystems at mkfs and/or mount time for best performance, so we don't have to require the system administrator to have to manually set mount options, mkfs options, and/or magic "echo" commands to /proc or /sys files. It would be great if we could get SATA and SCSI devices to also deliver these hints to kernel, or to have our kernels make some hueristics based on various SCSI mode pages, and then deliver it to the file system or via some defined /sys files so that userspace programs like mkfs can automatically DTRT. I'm not sure if this is going to require spec changes and hardware changes, or whether there are some existing hints form the device drivers that we might be able to leverage. For example, right now I'm just manually using the discard mount options on certain PCIe-attached flash where I know it's beneficial, but it's a manual tuning based on knowledge of the underlying storage device. Figuring out when it's better to use fstrim, or doing it at unlink time, etc., is something that's better done automatically instead of manually, but this is I fear answering questions like this in a reliable fashion is going to be a very hard problem --- and as storage devices get more complex, such as hybrid drives with even more varied and interesting performance characteristics, it's only going to get harder! - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
