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Conference ssag::ask_ssag

Title:	Ask the Storage Architecture Group
Notice:	Check out our web page at http://www-starch.shr.dec.com
Moderator:	SSAG::TERZAN

Created:	Wed Oct 15 1986
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	6756
Total number of notes:	25276

6728.0. "RAID degradation/rebuild metrics ???" by SAYER::ELMORE (Steve [email protected] 4123645893) Wed May 28 1997 20:27

        Are there any performance metrics on how much degradation occurs when
    a member of a SA450 RAIDset fails?  Related...are there guidelines on
    how long the recovery from a hot swap drive back to a replaced/repair
    RAIDset member takes?  

    I understand one can "adjust" the rebuild speeds, trading off levels of
    performance in doing so.  Is there more information like a white paper
    on this?

    Thanks,
    Steve

T.R Title User Personal
Name Date Lines

6728.1 No easy answer because of the parameters SSDEVO::RMCLEAN Thu May 29 1997 11:16 11

T.R	Title	User	Personal Name	Date	Lines
6728.1	No easy answer because of the parameters	SSDEVO::RMCLEAN		`Thu May 29 1997 11:16`	11
	The performance definately is not the same but it is VERY dependent upon the location of the data, the chunk size and the size of the raidset. If you have a 14 member raidset and you are only doing reads then only reads to the missing member will be slow. The others will be at full speed. Writes have a different characteristic in that the speed should be faster when the missing member is the parity member otherwise the writes should take about the same amount of time. As for the rebuild speeds I would recommend leaving it at the default unless you have a good reason to change it I.E. you are doing nothing else on the system and desire to get the rebuild done quicker.

The performance definately is not the same but it is VERY dependent upon the
location of the data, the chunk size and the size of the raidset.  If you
have a 14 member raidset and you are only doing reads then only reads to
the missing member will be slow.  The others will be at full speed.  Writes
have a different characteristic in that the speed should be faster when the
missing member is the parity member otherwise the writes should take about
the same amount of time.

As for the rebuild speeds I would recommend leaving it at the default unless
you have a good reason to change it I.E. you are doing nothing else on the
system and desire to get the rebuild done quicker.