StorView RAID Module
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C.2 Overwrite Data Area
The Overwrite Data Area (ODA) is a reserved area on the disk array used for storing data from logical
drives that are operating under a snapshot condition. They cannot be made visible as LUNs like other
logical drives.
Up to eight ODAs can be configured. Each ODA can have any capacity assigned to them and they can
be mapped onto any disk array with any RAID level (except RAID 6), chunk size and stripe size.
Once the ODA is created, snapshots can be taken on a logical drive at any time. Each logical drive can
have up to 24 snapshots issued.
ODA initialization is performed automatically by the RAID Controller during configuration. The user will
only need to provide one parameter during initialization and that is the ODA strip size. This defines how
much data that will be protected per copy on write operation. When the snapshot engine receives a write
command and has determined the underlying data must be protected, the size of the read and write
commands will be determined by the ODA stripe size. If the ODA stripe size is set to 128Kbytes, then the
protective read write will be done on 256 disk blocks at a time.
Overwrite Data Area, ODA
An internal storage area on an array that is dedicated to storing data
from a snapshotted logical drive. The data stored on the ODA is the
data from the logical drive that needed to be overwritten after a
snapshot was initiated. The ODAs are mapped on top of internal logical
drives. An ODA cannot be accessed externally through a host LUN.
They are only accessed internally.
Snapback
The process of restoring a logical drive from a selected snapshot. This
process takes place internally in the RAID controller firmware and
needs no support from any backup utility.
Snapshot
A method for producing a point-in-time image of a logical drive. In the
process of initiating a snapshot, no data is actually copied from the
snapshotted logical drive. However as new writes are made to a
snapshotted logical drive, existing data blocks are copied to the ODA
before the new data is written to the logical drive.
Snapshot Number
Identifier that references one of several snapshots of the same logical
drive.
Snapshotted LD
A logical drive that has one or more snapshots initiated on it.
ODA Size
The size of the Overwrite Data Area.
ODA Stripe Size
The read/write block size that the system will use when copying data
from the original logical drive to the ODA.
Virtual LUN or Snapshot LUN A special LUN created from a combination of the snapshotted logical
drives’ data and the data contained in the ODA.
Term
Description
Summary of Contents for 131018 - StorView Snapshot - Mac
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