Often there is performance tradeoff between large slower drives and smaller faster drives. SAS 15K drives provide phenomenal performance but their limited size can result in lack of usable disk space. Conversely, Near Line SAS drives offer huge amounts of usable space but their performance is lackluster. This performance gap can be filled using the CacheCade feature on some Dell PERC controllers that allow the use of SSD drives as read cache. For read intensive work loads, CacheCade can dramatically increase performance and allow the use of larger drive without sacrificing performance. I tested a variety of drive configurations, but for this blog I want to concentrate on two configurations. The 1st is a 1.8TB array using six 15K 600GB SAS drives. The 2nd is a 6TB array using four 3TB Near Line SAS drives and two SAS SSD drives. By utilizing CacheCade I was able to match performance of 15K SAS drives with NL-SAS drive and have over 3 times the storage available.
The drive arrays were test in a Dell PowerEdge R510 with a Dell PERC H700 RAID Controller in 1GB on non-volatile cache. I choose to use the 12 external plus 2 internal R510 configuration. For the CacheCade testing, the SSD drives were placed in the internal drive bays. The OS was loaded on a mirrored set of 146GB SAS drives. For performance testing Iometer was configured using the configuration test file found on Technodrone. The “RealLife-60%Rand-65%Read” access specification was used.
- 4 3TB Near Line SAS
- RAID 10
- Six 600GB 15K SAS
- RAID 10
- Four 3TB Near Line SAS
- RAID 10
- Two 200GB SAS SSD
- CacheCade using both SSD’s
The baseline NL-SAS configuration was able maintain 826 IOPS and sustain a throughput of 6.81MBps. Adding the two 200GB SAS SSDS and enabling them as CacheCade devices, increased this to 1531 IOPS and 12.54 MBps. This compared well with the 15K SAS configuration which produces 1567 IOPS and sustained 12.84MBps.
|Drive||IOPs Real Life Mix||MBps Real Life Mix|
|6TB NL SAS||
|6TB NL SAS + 2 SSD CacheCade||
|1.8TB with 15K SAS||