On Fri, Jul 20, 2012 at 12:36 PM, Goffredo Baroncelli <kreijack@xxxxxxxxx> wrote: > On 07/20/2012 09:15 PM, Josef Bacik wrote: >> SSD's do not gain anything by having metadata DUP turned on. The underlying >> file system that is a part of all SSD's could easily map duplicate metadat > > If I understood correctly you are stating that because an SSD *might* > "eliminates the benefit of duplicating the metadata" mkfs.btrfs *must* > remove _silently_ this behaviour on all SSD ? > > To me it seems too strong; or almost it should be documented in the man > page and/or issuing a warning during the format process. I'll have to second this .. this is my first time looking into btrfs - do feel free to correct me if my reading is not correct. Based on https://btrfs.wiki.kernel.org/index.php/Glossary, I assume the DUP is a flag to ask for meta-data duplication within the same device entity. This implies whenever an FS (meta-data) block is updated, the duplicated FS block needs to be modified as well (true ?). So within a conventional SSD firmware implementation, it is true that both FS blocks could end up in the same SSD block that get erased and re-allocated together. Similar thing could happen with disks that have embedded de-duplication feature turned on. However, this should have been a task for the admin (or whoever types this mkfs command). It is not a filesystem's job to assume how the firmware works and silently ignore the DUP request, *unless* there is a standard specification clearly describes linux devices that claim to be not "rotational" should behave this way. -- Wendy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
