Power Savings – No MAID Mystery Here
by Hu Yoshida on Sep 25, 2007
After our recent Power Savings Services announcement, James Rogers a Byte and Switch blogger posted the following, HDS’s MAID Mystery, in which he said that this sounds “suspiciously like MAID technology”. This is not MAID technology, in fact it can be considered the opposite of MAID Technology, so I posted the following comment on his blog, which I thought I should share here.
If you look up MAID storage in Wikipedia, it explains that MAID stands for a massive array of idle disks. It further states that it is designed for “write once, read occasionally” applications and “Compared to RAID technology a MAID has increased storage density, and decreased cost, electrical power, and cooling requirements. However, these advantages come at the cost of much increased latency, significantly lower throughput, and no or lower redundancy.”
The HDS Power Savings is an optional feature of our modular storage RAID arrays and is not a stand alone “massive array of idle (SATA) disks”. These HDS RAID arrays are production arrays that have no restrictions on writing or reading and can have high performance FC RAID groups and/or lower cost SATA RAID groups. Instead of keeping all the disks idle until they are accessed, this feature enables a user or scripted application to power down a RAID group when it is not being accessed and power it backup when it needs to be accessed.
This feature can provide lower cost through lower power and cooling,without the downside costs of “increased latency,significantly lower through put, and no or lower redundancy”.
So instead of powering up selected, slow, large capacity disks when they are accessed out of a pool of idle disks, Power Saving, enables you to power down selected RAID groups within a pool of spinning, high performance or large capacity, disks, when they are not being accessed. In a sense you could say that we took the opposite approach to MAID.
HDS did not want to limit power savings to large capacity disks. We assume that high performance disks as well as large capacity disks can be idled from time to time for power savings.
There still is a concern about the ability to monitor the health of idle disks. While PC’s, especially laptops, do this all the time without the protection of RAID, a data center environment requires a higher level of protection. We recommend the use of RAID 6 especially with SATA disks, to address the probability of multiple disk failures in a RAID group. We do not recommend RAID 0 for power savings RAID groups. During the idle period we wake up the disks for a periodic health check, and we check the health again on start up.
We offer this power saving feature through a services offering to ensure that our customers are thoroughly trained on the best practices in the use of this feature. If you are still concerned about the availability or reliability of disks that have been powered down. Than don’t use it. Unlike a MAID storage array where you must commit up front to invest in this technology, Power Savings is just an optional feature of our standard modular storage arrays.
So I hope you agree, there is no MAID mystery around our power saving service.
Comments (2 )
Looking forward to seeing this a little closer. Could potentially be great for some workloads/applications.
A bit more detail on how its implemented would be great.
MAID? Too little too late?
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