HPE 631681-B21 P420 2GB SmartArray Memory

HPE 631681-B21 2GB FBWC Kit for Smart Array P420 and P421 Controllers

The HPE 631681-B21 is a 2GB Flash Backed Write Cache (FBWC) option kit for HPE Smart Array P-series controllers, most often fitted to the Smart Array P420 and P421. It gives the controller a large protected cache so it can accept write requests quickly and keep that data safe if power is lost.

The kit pairs the 2GB cache module, spare 633543-001, with a capacitor pack and cable, listed as 660093-001. Together they let the controller enable write caching, which makes a clear difference to RAID 5 and RAID 6 write performance on ProLiant Gen8 servers.

Euroland IT Store lists this cache kit in New and Refurbished grades, offered subject to current stock.

HPE 631681-B21 Technical Specifications

What Is The HPE 631681-B21?

631681-B21 is the option kit number for the complete 2GB cache upgrade. Option kits are what HPE sells when a customer adds a feature to a server, so this kit includes everything needed for flash backed protection: the cache module that clips onto the controller and the capacitor pack that powers it during an outage.

The exact number matters because Smart Array cache modules come in several sizes and for several controller families. The 1GB version uses a different number, and later Gen9 and Gen10 controllers use different cache parts altogether. Ordering by 631681-B21 or by its module number makes sure you get the 2GB FBWC that the P420 and P421 expect.

How Flash Backed Write Cache Works

When write caching is on, the controller tells the operating system a write is complete as soon as the data reaches cache. The data is then written to the drives in the background. This is much faster than waiting for every disk, especially with parity RAID, where each write involves reading and recalculating parity.

The risk is power loss while data sits in cache. FBWC deals with this by using the capacitor pack to keep the module powered for long enough to copy the cache contents into on-board flash memory. When power returns, the controller restores the data and finishes writing it to the drives. Unlike older battery backed cache, there is no battery to wear out on a short cycle.

Without a working capacitor pack, a Smart Array controller will normally refuse to use write cache, as the data would not be protected. That is why the kit ships the capacitor with the module rather than as an afterthought.

New HPE 631681-B21

A New kit is a good choice when adding cache to a controller for the first time or when you want both the module and the capacitor in unused condition. Check the product page for the warranty on new stock.

Refurbished HPE 631681-B21

Refurbished kits suit administrators extending the life of Gen8 servers or replacing a failed cache after a controller warning. The condition and warranty of refurbished units are given on the product page.

Compatibility

• HPE Smart Array P420 controller
• HPE Smart Array P421 controller
• HPE ProLiant Gen8 servers fitted with one of these controllers

Check the controller model shown in the HPE Smart Storage Administrator or on the card itself before ordering. If you are replacing only a failed part, read the label on the existing module and capacitor, as you may need just one of the two components. Make sure the server has a mounting point for the capacitor pack and that the cable reaches it.

Related Part Numbers

• HPE 633543-001 is the 2GB FBWC module included in this kit, sold on its own as a spare.
• 660093-001 is the capacitor pack listed as part of the kit.
• HPE 631679-B21 1GB P-series FBWC is the smaller 1GB cache kit.
• HPE 631680-B21 1GB FBWC Smart Array is another 1GB cache item in the store.
• HPE 571436-002 Smart Array battery capacitor is a capacitor part listed in our catalogue; confirm it matches your controller before ordering.

Browse our RAID controller batteries and RAID controllers for related hardware.

How To Check This Is The Right Cache Kit

1. Identify the controller as a Smart Array P420 or P421.
2. Look at any existing cache module label for 633543-001 or the 2GB size.
3. Check whether the capacitor pack is present and healthy in the Smart Storage Administrator status page.
4. Confirm the server has a place to mount the capacitor near the controller.
5. Plan a maintenance window, as the cache module is fitted with the server powered off.

After Fitting The Cache

Once the module and capacitor are installed, power the server on and let the capacitor charge. The controller may show the cache as temporarily disabled until charging completes. Then use the Smart Storage Administrator to check the cache ratio between read and write, which you can tune to suit your workload. A database server usually benefits from more write cache, while a file archive may prefer a balanced split.

Buying HPE 631681-B21 in the UK

We supply storage and controller parts to businesses, IT teams, resellers and repairers across the UK. Condition, warranty, stock and delivery information for this kit are on the product page. UK mainland shipping costs nothing on orders worth more than £100 + VAT. Send us the controller model, server model and the part numbers on your existing cache or capacitor so we can confirm the match, or call 0203 209 6002.

Frequently Asked Questions

Which controllers is the 631681-B21 compatible with?

The kit is designed for the HPE Smart Array P420 and P421 controllers used in ProLiant Gen8 servers.

Does the 631681-B21 include the capacitor?

Yes, the kit is listed as the 2GB FBWC module 633543-001 together with capacitor pack 660093-001 and its cable.

Should I buy a New or Refurbished cache kit?

New gives you an unused module and capacitor, while Refurbished is a lower cost way to restore cache on an existing Gen8 controller.

What warranty is offered on this kit?

The warranty differs by condition and is shown on the product page for this item.

Can you deliver the kit across the UK?

Yes, we deliver throughout the UK, with free UK mainland shipping on orders over £100 + VAT and delivery details on the product page.