IBM Storwize V7000 Unified Problem Determination Manual page 262

Maintenance discharge cycles
Maintenance discharge cycles extend the lifetime of the batteries and ensure that
the system can accurately measure the charge in the batteries. Discharge cycles
guarantee that the batteries have sufficient charge to protect the Storwize V7000
Unified system.
Maintenance discharge cycles are scheduled automatically by the system and
involve fully discharging a battery and then recharging it again. Maintenance
discharges are normally scheduled only when the system has two fully charged
batteries. This condition ensures that for the duration of the maintenance cycle, the
system still has sufficient charge to complete a save of the critical data if the ac
power fails. This condition also ensures that I/O operations continue while the
maintenance cycle is completed. It is usual for both batteries to require a
maintenance discharge at the same time. In these circumstances, the system
automatically schedules the maintenance of one battery. When the maintenance on
that battery completes, the maintenance on the other battery starts.
Maintenance discharges are scheduled for the following situations:
v A battery has been powered on for three months without a maintenance
v A battery has provided protection for saving critical data at least twice.
v A battery has provided protection for at least 10 brown outs, which lasted up to
A maintenance discharge takes approximately 10 hours to complete. If the ac
power outage occurs during the maintenance cycle, the cycle must be restarted.
The cycle is scheduled automatically when the battery is fully charged.
Under the following conditions, a battery is not considered when calculating
whether there is sufficient charge to protect the system. This condition persists
until a maintenance discharge cycle is completed.
v A battery is completing a maintenance discharge.
v A battery has provided protection for saving critical data at least four times
v A battery has provided protection for at least 20 brown outs, which lasted up to
v A battery must restart a maintenance discharge because the previous
If a system suffers repeated ac power failures without a sufficient time interval in
between the ac failures to complete battery conditioning, then neither battery is
considered when calculating whether there is sufficient charge to protect the
system. In these circumstances, the system enters service state and does not permit
I/O operations to be restarted until the batteries have charged and one of the
batteries has completed a maintenance discharge. This activity takes approximately
10 hours.
If one of the batteries in a system fails and is not replaced, it prevents the other
battery from completing a maintenance discharge. Not only does this condition
reduce the lifetime of the remaining battery, but it also prevents a maintenance
discharge cycle from occurring after the battery has provided protection for at least
2 critical saves or 10 brown outs. Preventing this maintenance cycle from occurring
increases the risk that the system accumulates a sufficient number of power
outages to cause the remaining battery to be discounted when calculating whether
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Storwize V7000 Unified: Problem Determination Guide 2073-720
discharge.
10 seconds each.
without any intervening maintenance discharge.
10 seconds each.
maintenance cycle was disrupted by an ac power outage.