VA7410 AutoRAID

[Karthik S S]

Hi,

I have some questions on AutoRAID wrt VA7000 series of arrays.

1. What is the Highwater and Lowwater mark for moving the data from RAID1+0 to RAID5DP and vise versa. I read in some doc. that even when the array is fully utilized 10% of data is always stoerd in RAI1+0.

2. RAID5DP (Double Parity) : Do you have any equation on how to calculate P and Q parity and how to recover from single and double HDD failures?

3. Is RAID 5DP similar to compaq's RAID ADG??

Thanks,
Karthik S S

[Naveej.K.A]

Hi Karthik,

Pls have a look at what VA7000 series documentation has to say about your doubts.

1. In autoraid mode, the array controller attempts to place the data in the RAID level that provides the best performance based on how the host accesses data. This RAID level selection is both automatic and dynamic. Dynamic Data Migration isa background process and gives priority to host operation.
AutoRAID manages the data placement to the individual 256K block. Each LUN is divided into 256K blocks called clusters. A cluster can be stored in either RAID10 or RAID 5DP format. the virtualization data structure manage the translation of the LUN and the physical location. The controller is programmed to manage cluster placement. IT uses well known logic about RAID level performance characteristics and storage efficiency. This logic directs data that is frequently modified by small transactions to RAID10 storage. Data that is infrequently written, is driected to RAID5DP storage.

So i feel there could be some data blocks which are frequently accessed be stored in RAId10 in the event of array being full.

2. RAID5DP uses two algorithms to create two independent sets of redundacny data. This allows the array to reconstruct RAID5DP data in the event of two simultaneous disk failures. P uses an XOR(parity) algorithm. It is based on Reed-Solomom ECC technology, similar to error detection and correction found in ECCDRAM.

3. Don't have any idea.

With regards
Naveej

[Karthik S S]

This document was very useful,

http://www.hp.com/products1/storage/products/disk_arrays/infolibrary/mathematics_behind_RAID_5DP.pdf

-Karthik S S

[Uwe Zessin]

Hello Karthik,

here is a page about ProLiant array controllers:
http://h18004.www1.hp.com/products/servers/proliantstorage/arraycontrollers/documentation.html

Some of the link titles mention ADG, so there is a good chance that one of the documents describe ADG in more detail. Take another headache tablet and have fun!

[Karthik S S]

Uwe,

Thanks for the link. ADG is similar to RAID5DP

ADG=RAID5DP=RAID6 :-)

-Karthik S S