On 2019/12/17 21:34, Enrico Weigelt, metux IT consult wrote: > On 16.12.19 10:35, Carlos Maiolino wrote: > > Hi, > >>> Just curious: what's the exact definition of "zoned" here ? >>> Something like partitions ? >> >> Zones inside a SMR HDD. > > Oh, I wasn't aware that those things are exposed to the host at all. > Are you dealing with host-managed SMR-HDDs ? Yes. The host-managed models of SMR drives have become the de-facto standard for enterprise applications because of their more predictable performance compared to host-aware models. Many USB external disks these days also use SMR, but drive-managed models. These are regular block devices from the interface point of view: the host does not and cannot see the "zones" of the disk. SMR constraints are hidden by the device firmware. > >> On a SMR HDD, each zone can only be written sequentially, due to physics >> constraints. I won't post any link with references because I think majordomo >> will spam my email if I do, but do a google search of something like 'SMR HDD >> zones' and you'll get a better idea > > Reminds me on classic CDRs or tapes. Why not dealing them similarily ? Because of the performance difference. Excluding any software/use difference (i.e. GC overhead if needed), from a purely IO perspective, SMR host-managed disks are as fast as regular disks and can handle multiple streams simultaneously at high queue depth for better throughput (think video surveillance applications or video streaming). That is not the case for CDs or tapes. The performance difference with CDs and tapes, leading to different possible workloads and usage patterns, is even more pronounced with SSDs. In the end, only the write pattern looks similar with CDs and Tapes. Everything else is the same as a regular block device. > > > --mtx > > --- > Enrico Weigelt, metux IT consult > Free software and Linux embedded engineering > info@xxxxxxxxx -- +49-151-27565287 > -- Damien Le Moal Western Digital Research
