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Two questions:

  1. how, if at all, can I tell mdadm that the freshly created array needs no synchronizing because there is no data on it? I.e. basically force it into a state where it assumes that the "data" (i.e. the vast empty space) is synchronized and only synchronizes the meta-data?
  2. in case the above point isn't possible, why? Does the synchronization take into account the actual bad sectors or why would I have to synchronize an otherwise empty array?
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1 Answer

up vote 3 down vote accepted

You can use the --assume-clean option. From the man:

Tell mdadm that the  array  pre-existed  and  is
known to be clean.  It can be useful when trying
to recover from a major failure as  you  can  be
sure  that  no  data will be affected unless you
actually write to the array.   It  can  also  be
used when creating a RAID1 or RAID10 if you want
to avoid the initial resync, however this  prac‐
tice — while normally safe — is not recommended.
Use this only if you really know  what  you  are
doing.

When  the  devices  that  will  be part of a new
array were filled with zeros before creation the
operator  knows  the array is actually clean. If
that is the case, such  as  after  running  bad‐
blocks,  this argument can be used to tell mdadm
the facts the operator knows.
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Thank you. This is spot on. –  0xC0000022L Feb 11 '13 at 17:33
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