Spare Drives - HPE Smart Array P824i-p MR Gen10 User Manual

Full initialization
During full initialization, a complete initialization is done on the new configuration. You cannot write data to
the new logical drive until the initialization is complete. This process can take a long time if the drives are
large. This initialization overwrites all blocks and destroys all data on the logical drive.
Monitor the progress of the initialization process using the progress indicator.
No initialization
If you select this option, the new configuration is not initialized, and the existing data on the drives is not
overwritten. You can initialize the logical drive at a later time.
Regenerative writes
Logical drives can be created with background parity initialization so that they are available almost
instantly. During this temporary parity initialization process, writes to the logical drive are performed using
regenerative writes or full stripe writes. Any time a member drive within an array is failed, all writes that
map to the failed drive are regenerative. A regenerative write is much slower because it must read from
nearly all of the drives in the array to calculate new parity data. The write penalty for a regenerative write
is n + 1 drive operations where n is the total number of drives in the array. As you can see, the write
penalty is greater (slower write performance) with larger arrays.
This method has the following benefits:
• It allows the logical drive to be accessible before parity initialization completes
• It allows the logical drive to be accessible when degraded
Backed-out writes
After parity initialization is complete, random writes to a RAID 5, 50, 6, or 60 can use a faster backed-out
write operation. A backed-out write uses the existing parity to calculate the new parity data. As a result,
the write penalty for RAID 5 and RAID 50 is always four drive operations, and the write penalty for a RAID
6 and RAID 60 is always six drive operations. As you can see, the write penalty is not influenced by the
number of drives in the array.
Backed-out writes is also known as "read-modify-write."
This method has the benefit of faster RAID, 5, 50, 6, or 60 random writes.
Full-stripe writes
When writes to the logical drive are sequential or when multiple random writes that accumulate in the
flash-backed write cache are found to be sequential, a full-stripe write operation can be performed. A full-
stripe write allows the controller to calculate new parity using new data being written to the drives. There
is almost no write penalty because the controller does not need to read old data from the drives to
calculate the new parity. As the size of the array grows larger, the write penalty is reduced by the ratio of
p / n where p is the number of parity drives and n is the total number of drives in the array.
This method has the benefit of faster RAID 5, 6, or 60 sequential writes.

Spare drives

Dedicated spare
A dedicated spare is a spare drive that is dedicated to one array.
It supports any fault tolerant logical drive such as RAID 1, 10, 5, 6, 50, 60, and CacheCade SSD volumes.
The dedicated spare drive activates any time a drive within the array fails.
Features 19