On 2019/06/18 7:53, David Sterba wrote: > On Fri, Jun 07, 2019 at 10:10:15PM +0900, Naohiro Aota wrote: >> When in HMZONED mode, make sure that device super blocks are located in >> randomly writable zones of zoned block devices. That is, do not write super >> blocks in sequential write required zones of host-managed zoned block >> devices as update would not be possible. > > This could be explained in more detail. My understanding is that the 1st > and 2nd copy superblocks is skipped at write time but the zone > containing the superblocks is not excluded from allocations. Ie. regular > data can appear in place where the superblocks would exist on > non-hmzoned filesystem. Is that correct? Correct. You can see regular data stored at usually SB location on HMZONED fs. > The other option is to completely exclude the zone that contains the > superblock copies. > > primary sb 64K > 1st copy 64M > 2nd copy 256G > > Depends on the drives, but I think the size of the random write zone > will very often cover primary and 1st copy. So there's at least some > backup copy. > > The 2nd copy will be in the sequential-only zone, so the whole zone > needs to be excluded in exclude_super_stripes. But it's not, so this > means data can go there. I think the zone should be left empty. > I see. That's more safe for the older kernel/userland, right? By keeping that zone empty, we can avoid old ones to mis-interpret data to be SB. Alright, I will change the code to do so.
