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Keeping Cool with Hitachi Storage

by Hu Yoshida on Nov 17, 2010

Ever since David Floyer of Wikibon published the chart below, there has been a lot of interest in the dramatic reduction in power and cooling, which comes from our implementation of Small Form Factor, 2.5 Inch hard disk drives.

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Figure 1 – Comparison of Tier 1 Power & Space Costs over 3 years for a Performance Configuration (600GB drives, 2.5″ SAS where available otherwise 3.5″ FC drives)
Source Wikibon 2010

In addition to the 2.5 inch drives, we provide even better cooling and space improvements with our dense drive packaging. This package contains 128 x 2.5 Inch drives in a 13U high, 19-inch wide module, which you can see in the photo and drawing below. The cooling is done with fans that are mounted in the front and the back to push/pull air through the module. The fans are mounted on hinges that open out of the way when you need to work on the drives. When the fans on one side are opened to service a drive, the fans on the opposite side will increase speed to ensure optimum airflow. There are sensors which can vary the speed of the fans depending on the temperature.

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Prior to this, enterprise storage systems were designed for raised floors where cool air was pumped up from a plenum beneath the floor through holes in the floor tiles. Enterprise storage systems were designed like chimneys with disk drives mounted in the front and back with large fans which were mounted on the top to suck the air up through a “chimney’ in the middle of the frame. Air came up through the holes in the floor tiles at the bottom, and then sucked vertically up through the chimney, drawing in hot air from the sides and exhausting it out of the top.

Most modular, rack mount systems have a set of fans in the back of each drawer which pulls cool air in from the front of the drawer and exhausts it out of the back. The cool air can come from a raised floor plenum or can come from an overhead cooling system or rack mount cooling system sitting next to the storage racks. The disk drives are serviced from the front of the drawer, so the fans are positioned behind the disk drives and must be strong enough to draw air in from the front of the box and exhaust it out of the back.

The number of disk drives you can place in a drawer depends on the width of the disk modules and the width of the drawer. Most 19 inch drawers have around 12 to 15 disk modules and three fans for N+1 redundancy in the back. An exception is the dense drawer on the AMS 2000 modular storage array. While this drawer still has fans mounted in the back, the drawer can be pulled out with all the drives spinning so that the disks can be serviced from the top. This drawer can contain 48 x 3.5 inch SATA drives or 32 x 3.5 inch Serial Attach SCSI drives. Since SAS drives spin at a faster RPM than the SATA drives and require more cooling, the number of SAS drives is limited to ensure proper cooling with fans mounted in the back.

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The advantage of having fans mounted in the front and in the back of the disk drives on the Virtual Storage Platform (VSP) dense drive modules makes it easier to draw in air, so the fans can spin slower and draw less power. When you stand behind the VSP, you barely feel any heat or hear any noise. This configuration also enables the placement of VSP racks back to back to concentrate the AC on the hot rows and minimize the intermix of hot and cold air.

Although there are other many features in the VSP that can save CAPEX and OPEX, the savings in power and cooling are a no brainer.

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Comments (4 )

Roger Luethy on 18 Nov 2010 at 2:28 am

Good blog ! The cooling issues has more and more importance with the increased
density of 2.5″ Disksystems.

Vinay Babu on 18 Nov 2010 at 7:52 am

I have question by seeing the snaps above. There are 16 additional fans for push/pulling the air to the drive matrix. It may run slower at time but the number of fans are more. When compared to EMC array, fans are more here which will consume more power. Then how we are saving the power?

Hu Yoshida on 18 Nov 2010 at 8:54 pm

Vinay – Thank you for your question. I have not looked inside an EMC array recently, so I do not know how many fans are being used. In disk drawer enclosures, you usually have 15 drives that are cooled from behind with two fans plus an extra fan for n+1 redundancy. In our disk enclosure, we have 16 fans cooling 80 x 3.5 inch drives or 128 2.5 inch drives, which works out to a ratio of one fan per 5 x 3.5 Inch drives or one fan per 8 x 2.5 inch drives. This would work out to about the same number of fans per drive, except that our fans work in tandem for more efficiency.

Sindhia Naidu on 23 Mar 2011 at 5:14 am

Looking forward to the 2.5″ drives making it into modular space. This will mean that modular high destiny enclosure may not be required, as it will be possible to get the same number of disks in 4 RU made of 2 enclosures.
Lots of saving on power draw , space and weight.
I guess some of what the 2.5″ 10K spindles loses in rotational speed, is made up with better seek times.

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