On 2018-03-27 10:05 PM, Ali via cctalk wrote:
-------- Original message --------
From: Fred Cisin via cctalk <[email protected]>
Date: 3/27/18 5:51 PM (GMT-08:00)
To: "General Discussion: On-Topic and Off-Topic Posts" <[email protected]>
Subject: RAID? Was: PATA hard disks, anyone?
How many drives would you need, to be able to set up a RAID, or hot
swappable RAUD (Redundant Array of Unreliable Drives), that could give
decent reliability with such drives?
10 -
Two sets of 5 drive RAID 6 volumes in a RAID 1 array.
You would then need to lose 5 drives before data failure is imminent. The 6th
one will do you in. If you haven't fixed 50 percent failure then you deserve to
lose your data.
Disclaimer: this is my totally unscientific unprofessional and biased estimate.
My daily activities of life have nothing to do with the IT industry. Proceed at
your own peril. Etc. Etc.
-Ali
To meet Fred's original criteria you would only need 4 to create a
minimal RAID 6 array. In theory a RAID 1 array (mirrored) of 4 or more
disk could also survive a second disk failure as long as one copy of all
the pairs in the array survive but you are starting to play the odds,
and I know of some cases where people have lost . You can improve the
odds by having a hot spare that automatically take over for a failed
disk. One of the most important things is the array manager has to
have some way of notifying you that there has been a failure so that you
can take action, however my observations as a hardware support person is
that even when there is error notification it is often missed or ignored
until subsequent failures kill off the array. It also appears to be a
fairly common notion that if you have RAID there is no need to ever
backup, but I assure you RAID is not foolproof and arrays do fail. One
of the big problems facing using large disks to build arrays is the
number of accesses just to build the array may put a serious dent in the
speced number of accesses before error or in some cases even exceed it.
Paul.
