This article provides overview of the Storage Resource Pool in VMAX and the reference guide line of disk number in SSRP (Single Storage Resource Pool) when to choose MSRP (Multiple Storage Resource Pool) in VMAX array.

SRPs are comprised of one or more data pools, which contain the pre-configured data (or TDAT) devices that provide storage for the thin devices (TDEVS) that are created and presented to hosts or applications. The physical storage for the TDAT devices is provided by disk group, which contain physical drives. SRP contains following elements:

• Data Pools: A data pool, also known as a thin pool, is a collection of data devices of the same emulation and RAID protection type.
• Disk Groups: A disk group is a collection of physical drives sharing the same physical and performance characteristics. Drives are grouped based on technology, rotational speed, capacity, and desired RAID protection type.

A Storage Resource Pool (SRP) is the combination of above elements in VMAX. SRP is a collection of disk groups configured into thin data pools constituting a FAST domain whose performance and reliability is tightly coupled. This means that data movement performed by FAST is done within the boundaries of the SRP. Application data belonging to thin devise can be distributed across all data pool within the SRP to which it is associated.

By default, a VMAX3 storage array has a single SRP (SSRP) containing all the configured data pools. Through this SSRP configuration is appropriate for the vast majority of production environments, but SSRP system has some disadvantages. For example, SSRP system does not allow for physical isolation of drives. The may not only be required for regulatory and performance but also for fault tolerance reasons.

Fault Tolerance Reason:

A potential disadvantage with SSRP system is the risk of multiple drive failure affecting the entire system. Through this risk is extremely small and is almost completed by mitigated by the VMAX sparing mechanism which begins the process of replacing a failing physical drive with a permanent spares as soon as the HYPERMAX OS determines that it is likely to fail, but in system level, it do handling an unusually high I/O load, spare rebuild time are increased. This increases the chance, however small, that a second drive failure in the same SRP will cause an outage. Using RAID6 as the local RAID protection scheme when appropriate, using large drives, and configuring SRDF remote replication will mitigate these concerns, however, if SRDF is not being used and the disk group is large, multiple SRPs may be warranted. So EMC engineering considers the different disk and protection type and fault rate and provide following the list of disk number limitation of SSRP. This means once the single SRP contains disk exceeds the listing number, MSRP should be considered.

                                                                          

Size	Speed	7R5	3R5	R1	14R6	6R6	w   SRDF
200GB	EFD	368	928	2960	**	**	+
400GB	EFD	184	476	1576	**	**	+
800GB	EFD	96	244	838	**	**	+
300GB	15K	208	604	2134	4800	4800	+
300GB	10K	128	396	1436	4800	4800	+
600GB	10K	64	208	778	4800	4800	+
1200GB	10K	32	104	389	>3232	4800	+
2000GB	7.2K	8	24	144	3232	4800	+
4000GB	7.2K	No	8	72	1616	4800	+

Note: For the disk types which are not listed, you can contact your local service respective to have more information.

Multi-Tenant Situations Reason:

Multiple SRP system may be considered in multi-tenant situations where isolation of workload or dedicated physical drives is required. This segregation may be desired to prevent a tenant, who shares a single SRP with other tenants, from assigning high performing SLOs for multiple applications thereby potentially causing the performance to decline for others who share the SRP.

Multiple SRP will allow the physical disk to be isolated , but complete physical segregation of a specific SRP is not possible because VMAX hardware, aside from physical drives, will always be shared across the array regardless the configuration of the SRPs.

Legal Requirement Reason:

The need of segregate drives or data to adhere to legal requirement is another common and valid reason why multiple SRP array configurations may be adopted. Thought thing like DAEs, power, and engines will always be shared within the array, physical drives can be segregated to meet government or industry mandated physical data separation.

Performance Reasons:

Spindle isolation may also be required for performance reasons. Depending on the particular configuration, extreme performance requirements may require separate SRPs. For example, a configuration may be designed using a small number of flash drives with the remaining physical drives being 10k or 15k RPM with RAID1 protection in order to satisfy extreme performance requirements. A multiple SRP environment may also be warranted with certain operating system because of similar high performance needs. For example, SRPs for use with IBM I (formerly AS/400) may be designed in this way to isolate disk resources from what is being used by other operating system attached to the array.

Author: Fenglin Li

iEMC APJ

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