Hello, I would like to attend LSF/MM 2016 to discuss the following topics.
1) Online Logical Head Depop Some disk drives available on the market already provide a "logical depop" function which allows a system to decommission a defective disk head, reformat the disk and continue using this same disk with a reduced capacity. Such feature can allow reduced operation costs (delayed HDD replacement) but has the drawback of a data loss (data under the remaining valid heads) and disk downtime during re-formating. Online logical head depop is a proposed new feature allowing retaining the disk valid data and eliminating the need for a disk re-format. The basic idea is to introduce new commands for the host to discover the ranges of LBAs impacted by a defective head. Using this information, the host can take actions when a disk head failure event is suspected or reported: (a) The impacted LBAs can be depopulated, resulting in the disk operating as a “thin provisioned” device. (b) The impacted LBAs can be amputated, resulting in error for all subsequent accesses to the LBAs under the defective head. (c) Optionally, a host may decide to reformat (compact) the disk to restore operation as a fully-provisioned device with a lower capacity. The goal of the discussion would be to gather the opinion of the developers for drafting a command standard minimizing the impact of this feature on the block I/O stack as well as allowing a simple use of this feature by file systems and device mapper drivers (including logical volume manager). 2) Write back of dirty pages to SMR block devices: Dirty pages of a block device inode are currently processed using the generic_writepages function, which can be executed simultaneously by multiple contexts (e.g sync, fsync, msync, sync_file_range, etc). Mutual exclusion of the dirty page processing being achieved only at the page level (page lock & page writeback flag), multiple processes executing a "sync" of overlapping block ranges over the same zone of an SMR disk can cause an out-of-LBA-order sequence of write requests being sent to the underlying device. On a host managed SMR disk, where sequential write to disk zones is mandatory, this result in errors and the impossibility for an application using raw sequential disk write accesses to be guaranteed successful completion of its write or fsync requests. Using the zone information attached to the SMR block device queue (introduced by Hannes), calls to the generic_writepages function can be made mutually exclusive on a per zone basis by locking the zones. This guarantees sequential request generation for each zone and avoid write errors without any modification to the generic code implementing generic_writepages. This is but one possible solution for supporting SMR host-managed devices without any major rewrite of page cache management and write-back processing. The opinion of the audience regarding this solution and discussing other potential solutions would be greatly appreciated. Thank you. Best regards. ------------------------ Damien Le Moal, Ph.D. Sr. Manager, System Software Group, HGST Research, HGST, a Western Digital company damien.lem...@hgst.com (+81) 0466-98-3593 (ext. 513593) 1 kirihara-cho, Fujisawa, Kanagawa, 252-0888 Japan www.hgst.com Western Digital Corporation (and its subsidiaries) E-mail Confidentiality Notice & Disclaimer: This e-mail and any files transmitted with it may contain confidential or legally privileged information of WDC and/or its affiliates, and are intended solely for the use of the individual or entity to which they are addressed. If you are not the intended recipient, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it, is prohibited. If you have received this e-mail in error, please notify the sender immediately and delete the e-mail in its entirety from your system.