Dell PERC RAID Controllers

PERC stands for PowerEdge RAID Controller, and it is Dell's RAID card family. The naming is unusually informative once you know how to read it.

Reading a PERC model number

• Numeric generations - PERC 3, PERC 5, PERC 6, the earlier cards
• H-series - H200, H310, H330, H700, H710, H730, H800, H810, H840, the modern range
• Within the H-series the hundreds digit broadly tracks capability: the 200 and 300 cards are entry level, the 700 series is the mainstream cached controller, and the 800 series is external-facing
• An E suffix on the older cards, as in PERC 5/E and 6/E, means external ports for attaching a JBOD enclosure. An i means internal.

RAID mode and HBA mode

Not every PERC is a full RAID controller in practice. The entry-level cards, notably H200 and H310, are commonly used in HBA or IT mode, presenting disks directly to the operating system rather than hiding them behind a RAID volume. That is what software-defined storage and ZFS-style filesystems want; they need raw disks, and a RAID controller that insists on presenting volumes gets in the way.

Conversely, if you want hardware RAID with a battery-protected write cache, an entry-level card will not provide it - it has no cache to protect.

Cache and battery

Cached PERCs ship with 256MB, 512MB, 1GB or 2GB of write cache, protected by a battery or, on later cards, a flash-backed module. As with any cached controller, a failed battery causes a silent fallback from write-back to write-through and a sharp drop in write performance.

Before you swap

PERC stores array metadata on the drives, so a complete drive set moved to a compatible controller generally imports as a foreign configuration that can then be accepted. Treat that as a family characteristic rather than a guarantee, and never move an array without a restorable backup.

Send us the PowerEdge model and whether you need RAID or plain HBA behaviour and we will match the card, cache and cabling.