LSI SAS 2108 MegaRAID Power Save for Active/ Configured Drives
Today we are going to look at the LSI SAS 2108 power save feature for Active and Configured drives. For those wondering, the LSI SAS 2108 is an 8 port SAS 6.0gbps controller that supports parity RAID functions such as RAID 5. SAS 2108 cards can be found inexpensively as the IBM ServeRAID M5014 deal shows us. As I’m slowly setting up my new Home Server build, I’m starting to think about the long term use of the server. Its going to be on 24/7. Since money is not growing on trees, I need to keep the power bill to a minimum. My system main storage will be: 6x 2TB Hitachi 7k2000 Hard Drives in RAID5 each using 7.6w at idle = 45.6w total, I may at some point get 2 more and go RAID6. The RAID controller will be an LSI SAS 2108 based card.
45.6w at idle may not seem like a big deal as they consume about the same as 2x energy efficient light bulbs. Over a year it ads up. Let’s say 20 hours of idle a day = 912whr per day * 365 = 332.88Kwhr per year. In NZ each kwhr = about $0.25. That equals about $83.22 per year, just to keep the hard drives idle. $83 I can spend on other things like one beer a month for a year. Hitachi 7k200 drives are known for good performance and reliability but also noise. The disk noise is not excessive but audible all the same. Once the drives go into power save mode, there is a definite quieting from the server.
The LSI SAS 2108 is capable of power save mode for non-active and hot spare drives. All LSI SAS 2108 fimrware versions have these 2 options for power save mode. Firmware version 12.12.0-0048 for Sun/ Oracle brings us the ability to power save active drives also. Active drives are the drives in use and shown to the OS in an array be it single drive RAID 0 or a multi-drive RAID array.
I know most OS’s can do all this, turn drives off with power settings adjustments etc. But this is done via the controller. If you were booted in DOS, the drives would still power down. The only drawback is that spindled drives do take a few seconds to wind back up, so don’t expect instant access to your data. This is not meant for disks being accesses heavily 24/7.
The Dimmer Switch power save mode that the LSI MegaRAID is capable of (but only with Firmware v12.12.0-0048 from Sun/Oracle) also has the ability to cache activity to the drives while in power save mode. If the data fits in the cache the drives will not be spun up. This could be risky when the power is cut to the system and the cache is lost. Unless you are lucky enough to have the Cache Vault version of the LSI SAS 2108, or on a UPS that can last the power cut leaving data in drive cache may mean data loss. This do not read/write if data is or fits in cache can be turned off and data will not be cached while in power save mode.
I’m pretty happy with how it works and will probably use this in the build. This won’t be to everyone’s liking but hopefully for those that are interested this shows how one can do it. Now if only there was a newer version firmware for all cards that had this ability to use power save for active drives. For those wondering how to flash a SAS 2108 card, check the guide to flash the IBM ServeRAID 5014.