Using Intel® RAID controllers with Intel® Solid-State Drives (SSD) – Frequently Asked Questions
Q: What are the benefits of using SSD's in RAID?
A: Using SSD's in RAID configurations provide performance, availability, and capacity benefits compared to using a single SSD.
SSD's provide much higher random IO performance compared to regular HDDs – up to x100 on reads, and up to x10 on writes. In addition, average IO latencies are 10 to 100 times lower and sequential bandwidth is 50-100% higher with SSD's. These performance advantages allow replacing multiple HDDs with much smaller number of SSD's in many server or workstation applications. However, performance of a single SSD may still be insufficient for many applications, especially for write-intensive or sequential bandwidth hungry applications. Using RAID allows further scaling the SSD performance.
Availability and Data Protection:
SSD's don't have any moving mechanical parts and thus provide significantly higher reliability compared to mechanical HDDs. However, the flash memory and the controller electronics are still vulnerable to failures. Using mirrored (RAID 1/10) or parity (RAID 5) configurations reduces risk of data loss due to SSD failure and provides higher system availability. Higher performance of SSD's makes RAID rebuilds much faster, even under high workload, compared to mechanical HDD's. Short rebuild times with SSD's increase efficiency of the protection provided by RAID.
If an application requires capacity larger than a single SSD can provide, several SSD's can be used in a RAID configuration. In addition, Intel® RAID Controllers allow online capacity expansion by adding more SSD's to an existing RAID array without disrupting work of the SW applications.
Q: Are SSD's validated with Intel® RAID Controllers?
A: As of 6 Apr 2009, Intel® X25-E Extreme SATA Solid-State Drives have been validated with the current generation of the Intel® RAID Controllers. Other models of SSD's, including Intel® X25-M and X18-M Mainstream SATA Solid-State Drives, may be added to the validated list in future. For the most up-to-date compatibility information please refer to the Tested Hardware and Operating Systems list for the particular RAID controller model.
Q: Which RAID levels are optimal with SSD's?
A: In most cases RAID-5 will be optimal choice for server applications, providing well balanced combination of performance, capacity, data availability, and cost. More details on other RAID levels are provided below:
RAID-10: Can be used in business-critical applications that require the highest data availability and the highest write performance. RAID-10 can tolerate more than a single drive failure. However, benefits of using RAID-10 with SSD's are substantially smaller than with HDD's.
RAID-6: Not likely to be used with SSD's. Designed primarily for use with high-capacity HDDs that have long rebuild times.
RAID-1: Can be used when capacity of a single SSD is sufficient and when higher data availability and/or double the read performance are needed.
RAID-0: Can be used with workstation type of applications when potential data loss is not critical. Provides the highest performance and the highest capacity per dollar.
Q: What RAID settings are recommended with SSD's?
A: Optimal RAID settings are mostly the same as with HDDs:
Disk Cache Policy: Enabling disk cache improves write performance with SSD's substantially for some applications. However, it creates risk of data loss in case of power failure. Using UPS and redundant power supply is highly recommended when disk cache is enabled.
Write Policy: Write Back mode is recommended in most cases, especially with RAID-5. Using battery protection or UPS is highly recommended when Write Back is enabled to eliminate the risk of data loss in case of power failure.
Read Policy: No Read Ahead mode is recommended for the highest performance with multi-threaded applications. Always Read Ahead may be used for single-threaded sequential read workloads, for example, for backing up a data base.
Cache Policy: Direct IO mode is recommended in most cases.
This applies to: