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Array
In the RAID environment, data is striped across multiple physical hard drives. The array is
defined as the set of hard drives included in the data striping.
Data Scrubbing
Data Scrubbing forces all data sectors in a logical drive to be accessed so that sector media errors
are identified and corrected at the disk level using disk ECC information if possible, or at the
array level using RAID parity information if necessary. For a high level of data protection, Data
Scrubbing should be performed weekly.
Logical Drive
The array spcifies which drives should be included in the striping of data. Each array is
subdivided into one or more logical drives. The logical drives specify the following:
RAID-0
RAID level 0 stripes the data across all of the drives of the array. RAID-0 offers substantial speed
enhancement, but provides for no data redundancy. Therefore, a defective hard disk within the
array results in loss of data in the logical drive assigned level 0, but only in that logical drive.
RAID-1
RAID level 1 provides an enhanced feature for disk mirroring that stripes data as well as copies
of the data across all the drives of the array. The first stripe is the data stripe, and the second
stripe is the mirror (copy) of the first data stripe The data in the mirror stripe is written on
another drive. Because data is mirrored, the capacity of the logical drive when assigned level I is
50% of the physical capacity of the grouping of hard disk drives in the array.
RAID-5
RAID level 5 stripes data and parity across all drives of the array. When a disk array is assigned
RAID-5, the capacity of the logical drive is reduced by one physical drive size because of parity
storage. The parity is spread across all drives in the array. If one drive fails, the data can be
rebuilt. If more than one drive fails, but one or none of the drives are actually defective, then data
may not be lost. You can use a process called software replacement on the non-defective hard
drives.
Software Replace
A Software Replace of a hardfile refers to when the hardfile is not physically replaced in the
system. A drive may have been marked defunct but brought back online using the RAID
Administration program. The drive is rebuilt without having been physically replaced. This
could occur because when the RAID Adapter communicates with the hardfile and receives an
unexpected response, the adapter will mark the drive defunct in order to avoid any potential data
loss.
Synchronization
Synchronization reads all the data bits of the entire logical drive, calculates the parity bit for the
data, compares the calculated parity with the existing parity, and updates the existing parity if
inconsistent.
The following definitions describe the logical drive states for the IBM SCSI-2 F/W PCI-Bus
RAID Adapter and the IBM F/W Streaming RAID Adapter/A:
The adapters also assign device states to physical drives. The following definitions describe these device states:
DDD
The RAID adapter marks an ONL or OFL (RBL if ServeRAID) drive defunct, changing
its status to DDD and removing power from the drive, when one of the following
conditions occur:
DHS
A hot-spare or standby hot-spare drive (see below) enters the defunct hot-spare (DLIS)
state if it fails to respond to the adapter commands. Once a DHS drive is replaced, its state
changes from DHS to HSP. Only the IBM ServeRAID Adapter has the DHS state.
EMP
No device is present in the bay or the adapter cannot communicate with the drive. This
state is represented with dashes (- - -) on the IBM ServeRAID configuration screen, or a
blank space on the Administration and Monitor screen. Only the JBM ServeRAID
Adapter has this state.
FMT
Format: the drive is being reformatted.
HSP (IBM ServeRAID & ServeRAID II)
A hot-spare (HSP) drive is a drive designated to be a replacement for the first DDD drive
that occurs. The state of the drive appears as HSP. When a DDD drive occurs and a HSP
is defined, the hot-spare drive takes over for the drive that appears as DDD. The HSP
drive is rebuilt to be identical to the DDD drive. During the rebuilding of the HSP drive,
this drive changes to the RBL state. The RBL state will turn to ONL once the drive is
completely rebuilt and fully operating for the DDD drive.
HSP (Other controllers)
A hot-spare (HSP) drive is a drive designated to be a replacement for the first DDD drive
that occurs. The state of the drive appears as HSP. When a DDD drive occurs and a HSP
is defined, the hot-spare drive takes over for the drive that appears as DDD. The HSP
drive is rebuilt to be identical to the DDD drive. During the rebuilding of the HSP drive,
this drive changes to the OFL state. The OFL state will turn to ONL once the drive is
completely rebuilt and fully operating for the DDD drive.
OFL
Offline, a good drive that replaces a defunct drive in a RAID level I or level 5 array. This
drive is associated with the array, but does not contain any data. Drive status remains OFL
during the rebuild phase.
ONL
Online, a drive that RAID adapter detects as installed, operational, and configured into an
array appear as this state.
PFA
The firmware of a hard drive uses algorithms to track the error rates on the drive. The
drive alerts the user with a Predictive Failure Analysis (PFA) alert via the RAID
administration utility and NetFinity when degradation of drive performance (read/write
errors) is detected. When a PFA alert occurs, physical replacement of the drive is
recommended.
RBL
A drive in this state is being rebuilt. Only the IBM ServeRAID Adapter has this state. A
physical hard drive can enter the RBL state if one of the following conditions occurs:
A good working drive replaces a DDD drive that is part of the critical logical drive. At the
end of a successful rebuild, the state of the physical drive changes to ONL, and the state
of the corresponding logical drives changes to OKY.
The HSP or standby hot-spare (SHS) drive is added to the array and the state changes
from HSP or SHS to RBL. At the same time, the DDD drive is removed from the array
and its state changes to DHS from DDD. The adapter then automatically reconstructs data
in the RBL drive. The state of the corresponding logical drive remains CRT (if the RAID
level is 1 or 5) or OFL during the rebuild process. When the rebuild completes
successfully, the device state changes from RBL to ONL and the logical drive state
changes from CRT to OKY.
A ready (RDY) or standby (SBY) drive replaces a DDD drive that is part of the critical
logical drive. The state of the RDY or SBY drive becomes RBL. When the rebuild
completes successfully, the state changes to ONL. The DDD drive is removed from the
logical drive and becomes DHS
RDY
RDY appears as the status of a drive that the RAID adapter detects as installed, spun up,
but not configured in an array.
SBY
A standby drive is a hard disk drive that the RAID adapter has spun down. Devices such
as tape drives and CD-ROM drives are also considered to be in a standby state. Only the
IBM ServeRAID Adapter has the state.
SHS
A standby hot-spare is a hot-spare drive that the adapter has spun down. If a drive
becomes defrinet and no suitable hot-spare drive is available, a standby hot-spare of the
appropriate size spins up and enters the RBL state. You must have at least four hard disk
drives if you want a standby hot-spare with RAID-5. Only the IBM ServeRAID Adapter
has the state.
UFM
Unformatted, a drive that requires a low-level formatting before it can be used in an array.
You can start the low-level format by selecting Format Drive from the RAID
Configuration Main Menu.
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