Linux SATA RAID FAQ
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Many controllers on the market, or coming on the market are sold as "RAID controllers", but this term have become increasingly ambiguous over time.
- Sometimes the term refers to controllers where the OS driver is mostly unaware of the underlying disk devices attached to the controller. The OS driver only sees RAID arrays, and uses RAID-specific commands to read/write data. These controllers are what I call true hardware RAID.
- Sometimes the term refers to controllers where the OS driver and card's on-board flash BIOS provide 100 percent of the RAID capability. This is called software RAID, or less flatteringly, fake RAID.
- Occasionally, the term refers to controllers that have special features designed to enhance RAID, but still the OS driver must use normal ATA or SCSI commands to talk to the underlying disk devices. I classify these unique controllers as RAID accelerators, as they fall somewhere in between hardware RAID and software RAID.
FAQ questions and answers
- Is Intel ICH5/6/7 SATA really hardware RAID?
- Is VIA SATA really hardware RAID?
- Is Silicon Image (medley) SATA really hardware RAID?
- Is Adaptec 1210SA SATA really hardware RAID?
- Is Promise TX2 SATA really hardware RAID?
- Is Promise TX4 SATA really hardware RAID?
- Is Promise SX4 SATA really hardware RAID?
- (kernel 2.6) How do I access my RAID array data, which is stored in a vendor-proprietary format?
- (kernel 2.4) How do I access my RAID array data, which is stored in a vendor-proprietary format?
1. I have an Intel ICH5/6/7 SATA RAID. Why doesn't Linux support my hardware RAID?
A. It's not hardware RAID. It is software RAID, provided by the BIOS on the card.
2. I have a VIA SATA RAID. Why doesn't Linux support my hardware RAID?
A. It's not hardware RAID. It is software RAID, provided by the BIOS on the card.
3. I have a Silicon Image SATA RAID card. Why doesn't Linux support my hardware RAID?
A. It's not hardware RAID. It is software RAID, provided by the BIOS on the card.
4. I have an Adaptec 1210SA SATA RAID card. Why doesn't Linux support my hardware RAID?
A. It's not hardware RAID. It is software RAID, provided by the BIOS on the card.
5. I have a Promise TX2 SATA RAID card. Why doesn't Linux support my hardware RAID?
A. It's not hardware RAID. It is software RAID, provided by the BIOS on the card.
6. I have a Promise TX4 SATA RAID card. Why doesn't Linux support my hardware RAID?
A. TX4 has "RAID5 accelerator" features, but is not full and true hardware RAID. TX4 can offload RAID5 XOR calculations, but typically the host CPU is much faster. Therefore, Linux does not use the RAID5 features of this card.
7. I have a Promise SX4 SATA RAID card. Why doesn't Linux support my hardware RAID?
A. SX4 has extensive "RAID accelerator" features. While not true hardware RAID, this card has several features which do indeed accelerate RAID support. Unfortunately, Linux does not support the SX4's special RAID accelerator features at this time.
For certain configurations, Promise's Linux driver will perform better than the native Linux SATA driver.
8. Well, OK. I have figured out my card is not hardware RAID. How do I access the data stored by my BIOS software RAID, under a 2.6.x kernel?
A. Device Mapper ("DM") and dmraid. http://people.redhat.com/~heinzm/sw/dmraid/
9.How do I access the data stored by my BIOS software RAID, under a 2.4.x kernel?
A. Use the ataraid subsystem. See the Linux ATA RAID HOWTO for more information on ataraid in 2.4.x.