Data Availability

PERC Overview

The PowerEdge Expandable RAID Controller (PERC) is a high performance SCSI host adapter with RAID capabilities. The PERC provides reliability, high performance, and fault-tolerant disk subsystem management. It is an ideal RAID solution for Dell's workgroup, departmental, and enterprise systems and offers a cost-effective way to implement RAID in a server.

SCSI-based RAID

The Dell PERC is SCSI-based. It supports both LVD and SE devices. When LVD hard disks are used, throughput speeds of up to 160MB/sec and cable lengths up to 25m are possible. The PERC is a wide controller and as such can support up to 15 devices per channel.

CPU and Memory

PERCs feature their own CPU and memory. RAID functions are off-loaded from the server's CPU, freeing it to perform other tasks such as file sharing. The cache memory aids in performance by allowing data to be cached before it is written to the hard disks.

Hot-Swappable Hard Drives

The hard drives in most PowerEdge servers have the capability to be added or removed while the server is powered on, provided a PERC is in use and connected to a backplane that supports it. This allows for the removal or addition of hard drives without the need to reboot the server.

Configuration on Disk

RAID configuration is stored in Non-Volatile Random Access Memory (NVRAM) and on the hard disks themselves. This provides redundancy of the RAID information. This way, if the RAID card failed and had to be replaced, the replacement PERC would import the RAID information from the disk.