This item, 631679-B21, is the HPE retail number for the product described as 1GB P-series Smart Array Flash Backed Write Cache. Further details below.HPE Option Part #: 631679-B21HPE Spare Part #: n/aHPE Assembly Part #: n/aSpecifications:Product Type: Flash Backed Write CacheMemory Size: 1 GBApplication / Usage: ServerData Backup Type: FlashDimensions (W x D x H): 10.67 x 15.75 x 5.61 cm (4.2 x 6.2 x 2.21 in)Weight: 0.45 kg (1 lb)Compatible with:DL160 Gen8DL360p Gen8DL380p Gen8DL385p Gen8DL560 Gen8ML350p Gen8SL4540 Gen8SL4545 G7and possibly others