HP NetRAID 1 Controller - Manual (Page 18)

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Existing Installations Without Virtual Sizing Enabled
If you already are using the adapter without Virtual Sizing enabled, but now wish to add capacity to
an existing volume, you will be limited in your options. Here are the likely scenarios when Virtual
Sizing has not been enabled.
Without Rebooting
Unless Virtual Sizing is used, NT does not recognize new logical drives unless rebooted. Any drive
(logical or physical) will not be seen under the Disk Administrator until rebooted.
With Reboot
If a reboot is acceptable, then the server can be downed, Virtual Sizing enabled in Express Tools,
and the on-line expansion process under NT can be followed. This will allow a single drive to be
added to an existing array.
G. Alarm Feature
The adapters include an onboard tone generator to sound alarms and warnings. This alarm can be
enabled and disabled from the main menu. A list of audible alarm signals and their meanings is
located in the later section Audible Warnings.
H. Power Fail Safeguard Feature
One of the features of the HP NetRAID and HP NetRAID-1 adapters is reconstruction of an existing
array. Reconstruction is the process of modifying a RAID configuration by either adding a drive to
an existing array (e.g., capacity expansion) or migrating an existing array to a different RAID level
(e.g., changing from RAID 1 to RAID 5). Reconstruction should not be confused with “rebuilding”;
rebuilding is the process of recreating data on a replacement drive after a drive failure. Power Fail
Safeguard (PFS) allows the user to protect the disk array during the reconstruction process should a
power loss occur.
When a new array is initialized, the last one megabyte of each physical disk is reserved for use by
the adapter. Three blocks (sectors) are used to store configuration information and the remaining
area is used for the Power Fail Safeguard feature (the one megabyte of space is reserved even if PFS
is not enabled). When the PFS feature is enabled, the adapter uses the reserved space in the one
megabyte segment on each disk to temporarily store data which will be reorganized and written
during a reconstruction. Thus there will always be a copy of data which resides on disk during the
reconstruction process so there is no risk of losing any data. The data is reorganized to correspond
with the change in disk/RAID level associated with the reconstruction operation. Without PFS
enabled, the adapter reads data from the original set of disks into memory and then writes the
reorganized data to the disks. Because the data transitions through memory, there is a brief exposure
where data could be lost if a power loss occurs. The reconstruction process is not able to recover
data from memory after a power loss (even with battery backup). Enabling PFS will protect the
reconstruction process from any data loss in the event of a power failure. With or without PFS
enabled, a reconstruction will restart automatically where it was interrupted by a power failure.
Although PFS will protect the reconstruction operation, there will be a decrease in reconstruction
performance. When PFS is enabled, the reconstruction time will increase by a factor of about 2.5
times due to the extra overhead of always having data saved on disk. However, there will be no
affect on normal array performance (i.e., no reconstruction is active) with PFS enabled. A typical
reconstruction time for a 4 drive RAID 5 array using 2-gigabyte disks to a 5 drive RAID 5 array is
about 90 minutes with PFS disabled and no other data transfers. With PFS enabled, the same
reconstruction requires about 230 minutes.