Randy, On 2019/12/25 10:33, Randy Dunlap wrote: [...] >> +Sequential zone files can only be written sequentially, starting from the file >> +end, that is, write operations can only be append writes. Zonefs makes no >> +attempt at accepting random writes and will fail any write request that has a >> +start offset not corresponding to the end of the last issued write. >> + >> +In order to give guarantees regarding write ordering, zonefs also prevents >> +buffered writes and mmap writes for sequential files. Only direct IO writes are >> +accepted. There are no restrictions on read operations nor on the type of IO >> +used to request reads (buffered IOs, direct IOs and mmap reads are all >> +accepted). >> + >> +Truncating sequential zone files is allowed only down to 0, in wich case, the > > which > >> +zone is reset to rewind the file zone write pointer position to the start of >> +the zone, or up to the zone size, in which case the file's zone is transitioned >> +to the FULL state (finish zone operation). > > Just to clarify, truncate can be done to zero or the the zone size, but nothing else. > Is that correct? Yes, that is correct. That matches the drive processing of the REQ_OP_ZONE_RESET and REQ_OP_ZONE_FINISH requests which respectively reset the zone (file size down to 0) and transition the zone to full state (file size becomes zone size). [...] >> +# dd if=/dev/zero of=/mnt/seq/0 bs=4096 count=1 conv=notrunc oflag=direct >> +1+0 records in >> +1+0 records out >> +4096 bytes (4.1 kB, 4.0 KiB) copied, 1.05112 s, 3.9 kB/s > > why so slow? Indeed, that is really slow. I missed it :) The SMR drive I used for running this was probably in low power mode when I ran dd and needed waking up first, hence the slow response time. Running the same again, I get: dd if=/dev/zero of=/mnt/seq/0 count=1 bs=4096 oflag=direct conv=notrunc 1+0 records in 1+0 records out 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.000482601 s, 8.5 MB/s 0.5ms for a 4K direct write on an HDD, that looks OK to me (write cache is enabled on the HDD side). The same on a zoned null_blk device gives: dd if=/dev/zero of=/mnt/seq/0 count=1 bs=4096 oflag=direct conv=notrunc 1+0 records in 1+0 records out 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.00017558 s, 23.3 MB/s 175us for a single 4K direct write. Looks OK too. Thank you for all the typo & nit pointers. I will fix everything and post a v4. -- Damien Le Moal Western Digital Research
