HP StorageWorks Enterprise Virtual Array Online Firmware Upgrade Best Practices (5697-6388, January 2007)

Assessing the impact of I/O load on the upgrade

Because the online ﬁrmware upgrade is performed while host I/Os are being serviced, the I/O load

can impact the upgrade process. In general, performing the upgrade during a period of low I/O

activity will help ensure the success of the upgrade.

There are three primary ways in which I/O load impacts the online upgrade process.

• First is the ability of the storage system to perform the upgrade in pa rallel with host I/O. These

two processes compete for internal controller resources, with host I/O having the higher priority.

Therefore decreasing the host load, by ﬁnding a period of time where host demand is the

smallest, allows a greater number of resources to be used to execute the online controller ﬁ rmware

upgrade a

s quickly as possible.

• Second is the ability of the storage system to communicate with HP Command View EVA. The ﬁrst

steps of the ﬁrmware upgrade use a process that has a lower priority than host I/O. Under heavy

I/O load, the time required to perform the upgrade can exceed the timeouts expected by HP

Command View EVA for the completion of the upgrade process. Althoug h the ﬁrmware upgrade

is typically successful, the timeouts may cause HP Command View EVA to lose connectivity to the

storagesystemandcancauseconfusionintheupgradeprocess.

• Third

is the queuing effect on host I/O. During the controller resynchronization interval, I/Os ca n

conti

nue to queue on the host. This creates a backlog of requests that must be processed by the

stora

ge system when the ﬁrmware upgrade is complete. Although the resynchroniza tion interval

may b

e less than 60 seconds, a large backlog may require a great deal of time to clear, and

some

hosts may experience I/O time outs.

As a result of these factors, it is recommended that an evaluation of the workload b e done before

performing the upgrade. This will help identify periods of low I/O activity during which the upgrade

can be performed successfully.

Selecting an appropriate time to perform the online upgrade

To ensure the succ ess of an online upgrade, selecting the appropriate time is essential. Selecting a period

of low I/O activity will ensure the upgrade completes as quickly as possible, and will avoid disruptions to

host and applications due to timeouts. Attempting to upgrade a storage system that is in the middle of

processing a large I/O intensive batch job will likely causes hosts to lose connectivity with the storage

system. Consequently, ﬁnding an appropriate time for the upgrade is very important.

The number of disk drives in the storage system inﬂuences the I/O demands that are tolerable d uring an

online ﬁ rmware upgrade. HP recommends that during an online upgrade the I/O demand on the storage

system be limited to the values shown in Figure 1, Figure 2, Figure 3,andFigure 4. The load values for

both the number of IOPS and throughput (MB / s) must be not be exceeded.

For example, an EVA8000 with 168 disk drives should have a demand less than both 70 MB/s and

7,000 IO PS and an EVA5000 with 168 disk drives should have a demand less than both 40 MB/s and

4,000 IOPS. This will ensure that a healthy storag e system can resynchronize well with in the deﬁned

resynchronization window.

HP StorageWorks Enterprise Virtual Array online ﬁrmware upgrade best practices