dk, There is a good document on the subject on Powerlink titled 'EMC CLARiiON Global Hot Spares and Proactive Hot Sparing Best Practices Planning'. I think that it has one of the longest titles for one of the shortest Best Practices documents... but it has the information you are looking for.  In short, the FLARE code does not use the rotational speed of the disk in deciding which hot spare to use. FLARE will attempt to pick a hot spare on the same bus as the failed drive, but since there is only one bus your array I don't know if the algorithm will further narrow the selection down by enclosure. If you are concerned about the reduced performance from using a 10k drive as a hot spare for 15 drives then you could just delete the 10k hot spare and just use the 15k hot spare. EMC recommendsa 30:1 ratio for disks to hot spares, so with the one 15k drive in place you still meet this best practices ratio.  Aran
CX3-10, originally single tray of 300 GB 10K RPM FC disks. Adding a second DAE with 300 GB 15K RPM FC disks (obviously a single bus so both will be forced to 2Gbps, understood). The original DAE has an existing (10K) hot spare provisioned.  When provisioning a new 15K hot spare, since both 10K & 15K disks are the same size and both are FC, in the event of disk failure, can it differentiate RPM class and know to use only the 15K to rebuild an RG of 15K disks (and ideally only the 10K for the 10K RG, since I don't want to waste a 15K disk on this)? If it can't tell the difference, does that mean I need to go with only 15K hot spares to guarantee only 15K disks will be used with other 15K RGs? Or is there some other way to isolate?  Thanks! dk
Hot Spares 15K & 10K RPM