On Tue, 18 Jun 2013 16:52:09 +0400 Роман Алексеев <r.alekseev@xxxxxxxxx> wrote: > Hello, > > I want to speed up rebuilding process of the raid to do that I'm going > to apply the command: > > mdadm --grow --bitmap=internal --bitmap-chunk=NNNN /dev/mdX > > But I don't know how to calculate optimal value of bitmap-chunk option. > How can I do that? It's just the minimum granularity of pieces that get rebuilt after unclean shutdowns. E.g. if your array decides it's "dirty" in 5 different areas, with a 16MB chunk the rebuild will process 5*16MB, but with a 128MB it will rebuild 5*128MB. On modern systems the difference in time required to do the rebuild between these two will be negligible. But having a larger size helps noticeably in everyday operation (makes writes faster). So there is nothing to "calculate" really, just use a reasonably large size like 128 or 256 MB. https://raid.wiki.kernel.org/index.php/Write-intent_bitmap http://techblog.tgharold.com/2013/01/mdadm-using-bitmaps-to-speed-up-rebuilds.html http://blog.liw.fi/posts/write-intent-bitmaps/ (the 1st comment) -- With respect, Roman
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