為了這個問題..
在DELL網站查了老半天...

http://support.dell.com/support/edo...omss/ecache.htm

CacheCade is used to improve random read performance of the Hard Disk Drive (HDD) based Virtual Disks. A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent data. SSDs significantly increase the I/O performance (IOPS) and/or write speed in Mbps from a storage device. With Dell Storage Controllers, you can create a CacheCade using SSDs. The CacheCade is then used for better performance of the storage I/O operations. Use either Serial Attached SCSI (SAS) or Serial Advanced Technology Attachment (SATA)SSDs to create a CacheCade.

Create a CacheCade with SSDs in the following scenarios:
Maximum application performance—Create a CacheCade using SSDs to achieve higher performance without wasted capacity.
Maximum application performance and higher capacity—Create a CacheCade using SSDs to balance the capacity of the CacheCade with high performance SSDs.

Higher capacity—If you do not have empty slots for additional HDDs, use SSDs and create a CacheCade. This reduces the number of HDDs required and increases application performance.

The CacheCade feature has the following restrictions:
Only SSDs with the proper Dell identifiers can be used to create a CacheCade.
If you create a CacheCade using SSDs, the SSD properties are still retained. At a later point of time, you can use the SSD to create virtual disks.
A CacheCade can contain either SAS drives or SATA drives but not both.
Each SSD in the CacheCade does not have to be of the same size. The CacheCade size is automatically calculated as follows:

CacheCade size =capacity of the smallest SSD * the number of SSDs
The unused portion of SSD is wasted and can not be used as an additional CacheCade or an SSD-based virtual disk.

The total amount of cache pool with a CacheCade is 512 GB. If you create a CacheCade which is larger than 512 GB, the storage controller still uses only 512 GB.

The CacheCade is supported only on Dell PERC H700 and H800 controllers with 1 GB NVRAM and firmware version 7.2 or later.

In a storage enclosure, the total number of logical devices including virtual disks and CacheCade(s) cannot exceed 64.


這根本整死人...
PFK塞到1GB NVC Cache..
DELL的官方PDF文件根本沒講清楚.......