Thread (10 messages) 10 messages, 8 authors, 2007-03-26

Re: Swap initialised as an md?

From: Bill Davidsen <hidden>
Date: 2007-03-26 03:45:53

Michael Tokarev wrote:
Bill Davidsen wrote:
[]
  
quoted
If you use RAID0 on an array it will be faster (usually) than just
partitions, but any process with swapped pages will crash if you lose
either drive. With RAID1 operation will be more reliable but no faster.
If you use RAID10 the array will be faster and more reliable, but most
recovery CDs don't know about RAID10 swap. Any reliable swap will also
have the array size smaller than the sum of the partitions (you knew that).
    
You seems to forgot to mention 2 more things:

 o swap isn't usually needed for recovery CDs
  
That's system dependent, but at least two report problems with swap if 
configured as RAID10. Confusing error messages are not a plus when you 
get to the stage of using a recovery CD. The need for swap depends on 
configuration.
 o kernel vm subsystem already can do equivalent of raid0 for swap internally,
   by means of allocating several block devices for swap space with the
   same priority.

If reliability (of swapped processes) is important, one can create several
RAID1 arrays and "raid0 them" using regular vm techniques.  The result will
be RAID10 for swap.
Sorry, no. It will be RAID0+1, not the same thing. See RAID10 description.

-- 
bill davidsen [off-list ref]
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979
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