Song Liu <songliubraving@xxxxxx> writes: >> >> Hmm, perhaps this should instead follow the same command line mechanics >> as "--write-mostly" whereby all the devices listed after that flag take on that >> role. Also, if we anticipate more roles I wonder if the option should be "-- >> role=" that assigns the given role to the device(s) that follow. >> >> Thoughts? >> >> I'm looking at this from the perspective of reviving the SRT patches [1] where >> a role for a read/write cache device is needed. Where a read/write-cache is >> different than a journal. >> >> [1]: >> https://urldefense.proofpoint.com/v1/url?u=https://lwn.net/Articles/59661 >> 4/&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=J3jGe56dIPfS5TN6DM82U >> YbbeR1j2viaiSJI40tv6lE%3D%0A&m=dv5znFd%2BTZdHZaSKjzBVqJbdtNBALR0 >> RgzhZsOmsWAU%3D%0A&s=80c812981ff98264cf1bb2b79032863d4e33ba100 >> 093d41956eab3fbd33b5635 > > I think --write-mostly is used as _hint_ to RAID 1 that differentiates SSD from > HDD. While --write-journal turns on "MD_FEATURE_JOURNAL" and specifies > journal device. We should not need more than 1 journal device. In this sense, > I think current --write-journal works well... --write-mostly isn't a hint. It is a clear statement that these devices should only be read from if there is no other option (the original justification had nothing to do with SSDs). However a write journal is a very different thing to the other devices. For example it is not counted in the --raid-disks and --spare-disks where as all other devices (whether --write-mostly or not) are. If anything --write-journal is more like a --bitmap=/some/file than --write-mostly. So, I'm happy for --write-journal to stay as it is. Thanks, NeilBrown
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