RFD: question/probe regarding adding dump-levels A-Z after 0-9 for xfs{dump,restore}

How difficult would it be to allow 26 more dump levels in xfs dump/restore? Theoretically anyone using 0-9 would see no change. Would there be some "problem" or "gotcha" in adding in what would _seem_ to be a simple change?

thanks,
-linda

Everything _seems_ simple with xfsdump. e.g. the inventory session headers supports up to 255 levels in it's on-disk format, but the xfsdump command is limited to just 10 levels by a separate "max level" define.

IOWs, on the surface it _seems_ simple to change it, but I don't know all the places that the dump level is stored, nor what would happen if an older xfsdump/xfsrestore binary tripped over an inventory with a dump level larger than they were compiled to handle.

I also don't know if there are scalability problems with resolving the contents of incremental dump levels. Certainly restoring from 30 incremental dumps is more onerous than 6-7, but that's just time. What I don't know is how the invenetory scales to more than 10 incremental and whether there's some exponential algorithm in there that falls apart. So there's a lot of testing that would be needed to validate what looks like a 1 line change to the code.

So, yes, technically we could increase the dump level, but there's a *lot* of verification work after doing so and it's not a risk-free modification.

FWIW, the idea behind 10 dump levels is that it is enough for a full dump every week w/ an incremental every night of the week until the next full dump is done on the weekend. What's the backup plan you want to use/need that requires a larger number of incrementals? Knowing what you want more dump levels for helps us understand how it would be used and what really needs to be testedi first....

Cheers,

Dave.

Dave Chinner
[email protected]