631681-B21 is the HPE option part number for 2GB P-series Smart Array Flash Backed Write Cache. It is the orderable option identifier for a 2GB RAID controller cache memory module with flash backed write cache, used with HPE P-series Smart Array controllers. If you are specifying a build or expanding an existing configuration, this is the number that typically appears on quotes and configuration sheets. Listed server compatibility covers DL160 Gen8, DL320e Gen8, DL360e Gen8, DL360p Gen8, DL380e Gen8, DL380p Gen8, DL385p Gen8, DL560 Gen8, ML310e Gen8, ML310e Gen8 v2, ML350e Gen8, ML350p Gen8, SL4540 Gen8 and SL4545 G7.
HPE Option Part #: 631681-B21
HPE Spare Part #: 633543-001
HPE Assembly Part #: 610675-001
PRODUCT SPECIFICATIONS FOR 631681-B21:
- Product Type: RAID controller cache memory
- Cache Memory Capacity: 2GB
RESOURCES FOR 631681-B21
Quickspecs for 631681-B21COMPATIBLE WITH:
PROLIANT DL SERIES
PROLIANT ML SERIES
PROLIANT SL SERIES
** This list may not be complete. Contact us via Live Chat if you have any questions about compatibility.
FREQUENTLY ASKED QUESTIONS ABOUT 631681-B21
What is the difference between 631681-B21 and 633543-001?
They identify the same physical product under different HPE numbering schemes. This page, 631681-B21, is the option part number, which is the orderable configuration identifier. 633543-001 is the spare part number, used for service replacement of the same module. This family also includes one assembly revision, shown in the cross-reference block on the page. An assembly part number identifies the built module as manufactured, rather than how it is ordered or stocked for service.
What capacity and function does this module provide?
631681-B21 provides 2GB of RAID controller cache memory for HPE P-series Smart Array controllers. It is a flash backed write cache module, meaning cached write data is preserved to flash rather than depending on continuous battery-maintained volatile memory. For configuration purposes, treat it as the 2GB cache option in the P-series Smart Array cache lineup and match it to a controller that accepts P-series flash backed write cache.
Which servers is 631681-B21 listed as compatible with?
Listed compatibility covers HPE DL160 Gen8, DL320e Gen8, DL360e Gen8, DL360p Gen8, DL380e Gen8, DL380p Gen8, DL385p Gen8, DL560 Gen8, ML310e Gen8, ML310e Gen8 v2, ML350e Gen8, ML350p Gen8, SL4540 Gen8 and SL4545 G7. If your platform is not on that list, verify against the HPE QuickSpecs for your server and the specific P-series Smart Array controller installed before ordering.
Will the part I receive be labeled 631681-B21?
Not necessarily. HPE option numbers such as 631681-B21 identify how a part is ordered, while the physical module and its label may carry a spare number or an assembly revision number instead. All of those numbers refer to the same 2GB P-series Smart Array flash backed write cache. Where a system builder assigns its own catalog identifier, that is an OEM model number and describes the same hardware under a different brand's numbering.
HPE PARTSURFER INFO FOR 631681-B21
| Spare PN | Description | |
|---|---|---|
 | 633543-001 | 2GB flash backed write cache (FBWC) memory module, 72-bit wide - Part does not include the controller board or capacitor module - For use with the P420, P421, P430, P431, 822, and 830 Smart Array controllers |
| 660093-001 | Capacitor pack with 914mm (36 in) cable. For use with 512MB/1GB/2GB cache module - Provides back up power to the flash-based write cache (FBWC) memory module for up to 80 seconds in the event of a system power failure. For use with Smart Array controllers |
Last Updated: 2026-05-27
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This product is warrantied against hardware failure for a period of 1 Year from the date of purchase. Before making a purchase, please take a moment to review our return policy below.
Returns
It is the customer's responsibility to verify compatibility with their machine(s) before placing an order. If an item is ordered by mistake, it can be returned for refund, minus a 25% restocking fee, within 5 business days of receipt. The cost of freight is not refundable.
Please be aware that factory-sealed equipment can only be returned if it remains unopened.
Defective Products
If you have received a defective part and your machine is still within the HPE warranty period, please initiate a warranty exchange by visiting the HPE Enterprise Support Center. Be sure to have the serial numbers of the defective drive and your server/storage array handy.
In case your hardware becomes defective during the Global One warranty period, but the HPE warranty has expired, you can return the product to us for a working replacement. You are responsible for the shipment of returned merchandise. However, we will cover the expense of Ground /Economy shipment for the replacement item(s).
Requesting an RMA
To initiate a return or warranty claim, please complete and submit the RMA Request Form.
