Part numbers: 078-000-079 (EMC VPLEX) · 81Y2432 (IBM DS5020) · 5541807-A (HDS VSP 9500)
Start with something most people have never thought about.
A battery is the only spare that degrades while doing nothing.
A controller, a mainboard, a network card — keep them dry and static-safe and they will sit on a shelf for five years and still work. A battery will not. A lithium cell starts ageing the day it leaves the factory, and sitting in a warehouse with no charge-discharge cycle, three years later its capacity may be down to 60–70% of nameplate, sometimes less.
So for batteries, “we have that part number in stock” is not a sufficient statement.
These three part numbers do the same job
| Part number | Equipment |
|---|---|
| 078-000-079 | EMC VPLEX standby power battery |
| 81Y2432 | IBM DS5020 controller cache battery |
| 5541807-A | HDS VSP 9500 cache battery |
Three different vendors, three completely unrelated part numbers — but their role in the system is identical:
during the few tens of seconds after an unexpected power loss, hold on to the data that is still in cache and has not yet been written to disk.
For performance, storage puts incoming host writes in memory cache, acknowledges them, and destages to disk afterwards. There is a window in between. If the room loses power in that window, that data is in volatile memory and is gone — unless a battery holds the controller up long enough to flush it to flash or a local disk.
The battery is insurance bought for those few tens of seconds.
What happens when the battery fails
Nothing, immediately. That is exactly what makes it awkward.
When the system detects a battery fault or insufficient capacity, it makes the conservative choice: it disables the write cache. From then on every write goes straight to disk and is only acknowledged once it lands.
The data is safe. The price is write latency going from sub-millisecond to tens of milliseconds. What the business sees is “the system suddenly got sticky, but nothing is reporting an error.”
So the hunt starts: hosts, database, switches — and it ends at one battery inside the array.
Three things to ask when sourcing a battery
1. Manufacturing date and batch. A part number alone is not enough. A cell manufactured in 2019, even brand new and sealed, can report low charge the day you install it. Whether a supplier is willing to give you the date tells you most of what you need to know about them.
2. Is it included with the part? On some equipment the battery is a separate FRU; on others it is built into the controller. For the V5000 node canister, the vast majority of units in circulation are bare, with no battery — and that gets discovered when the engineer and the part are already in the data hall and the battery has to come off the old unit. Confirm it beforehand or the job does not finish that day.
3. How is the warehouse storing them? Batteries age faster in heat. Whether a spare-parts warehouse has climate control is the difference between “in stock” and “in stock and usable”.
Afterwards
For parts like this our rule is: stock what can go straight into a machine, not just the part number.
Every battery in our warehouse carries its manufacturing date, and anything past its window is rotated out on a schedule rather than discovered when a customer asks. Because by the time a customer comes looking for a battery, they are usually already running on a single controller with zero redundancy — and that is not a moment to gamble twice.
The mechanisms described here are compiled from the vendors’ public documentation. For any specific machine, go by what the system actually reports on site and by the official documentation for that code level. Case details have been merged and anonymised.
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