How about an option to create a one-time RAID1 mirror on top of existing
raid structure? What it really is, is a backup. Install necessary drives,
trigger mirroring, remove drives, and array goes back to previous state
without additional mirror.
Beats backing up multi-tera-bytes to floppies. :-)
BobH
-----Original Message-----
From: Tony Mantler [SMTP:nicoya@xxxxxx]
Sent: Tuesday, September 07, 2004 11:53 AM
To: linux-raid@xxxxxxxxxxxxxxx
Subject: Concatenation with redundancy
Hello,
Recently I've seen a growing trend in creating very ad-hoc storage
arrays for storing large quantities of media files (videos, music,
etc). These arrays are usually initially created with a small number of
concatenated drives, say 2 or 3, but over time can easily grow to span
6 or 8 drives as personal budgets allow.
Obviously as time goes by the exposure to a single drive failure taking
down the whole filesystem increases considerably, and I've seen this
happen a number of times. Due to the size (frequently 1-2tb) and nature
of data on the array, backup is usually impractical.
It would seem that the current options for combining redundancy with
flexible expansion capability leave a little to be desired. RAID 10
presents far too much wasted space for this type of application, and
RAID 50 offers much less flexibility than is desired, and is still too
inefficient for the number of drives in question.
Thus the idea came to me for creating a somewhat new RAID level, which
would be a concatenation with dedicated parity. Call it RAID 4C maybe,
as in "RAID 4, but concatenated rather than striped".
Thus, the data would appear as thus:
drive 1 drive 2 .. parity drive
block 1 ~ block N+1 .. = parity 1
block 2 ~ block N+2 .. = parity 2
..
block N ~ block N+M .. = parity N
This would allow for inserting new drives without mangling the block
order, thus preserving the data on the array. Ideally it would also be
possible to create a heterogeneous array by ensuring that the parity
drive was equal to or larger than the largest data drive, and assuming
zeroed blocks for all non-present sectors.
So, am I smoking crack here? Does anyone think this would be worth
implementing? Has this already been implemented and I just haven't seen
it?
Cheers - Tony 'Nicoya' Mantler :)
--
Tony 'Nicoya' Mantler -- Master of Code-fu -- nicoya@xxxxxx
-- http://nicoya.feline.pp.se/ -- http://www.ubb.ca/ --
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