3PAR virtualization concept

[TurbinYA]

I don't understand concept "set size -> step size -> row size -> number of rows".  We can see information about this parameters in "3PAR Architecture", "3PAR Concepts Guide" and if set size, step size and row size parameters seems easy for understanding - "number of rows" like mist for me.

Why we need more then one row of LD? Why 3PAR restrict maximum row size for RAID1/10? When it is necessary to use more than one row?

Yaroslav.

UPDATE.

Maximum row size restriction - 40 sets - still valid for all RAID types or only RAID1/10?

[Dennis Handly]

>I don't understand concept "set size -> step size -> row size -> number of rows".

Set size is related to RAID level.  Step size is how the data is mapped to the region.

>Why 3PAR restrict maximum row size for RAID 1?

I assume there is no benefit for making the row larger.

[TurbinYA]

>I assume there is no benefit for making the row larger.

This sounds very abstract. We can use more then one row for RAID1/10. Why we can't use one long row?

[Sheldon Smith]

In regards to Row Size, that just defines how many “raid sets” make up an LD. So, for example, if you have an array and there were 160 HDDs behind a node pair, when we go to create a RAID5 3+1 LD we will break the 80 HDDs behind the node into 20 sets of four disks giving us a row size of 20.

There is NO reason to mess with row size; it is driven by the raid set size and the number of disks behind the node. 

Note: While I work for HP, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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[TurbinYA]

Sheldon, thak you for answer.

1. I disagree, that no reason to mess with row size.

In this document 3PAR and VMware best practices we can find: The default CPG row size (RowSz) is smaller/not balanced when compared to the tuned CPG. I think it's good practice, then you understand how system work.

2. How many rows can have LD? One? Two rows - two LD? In row chunklet always places in different disks or system try do this and if can't place chunklets to same disk?

3. Why row size restrict 40 sets? This restriction work for all RAID's of only for RAID1/10?

Anyone understand how it's work in 3PAR?