Does 15K SAS still make cents?

I am sure there are occasions where drive performance doesn’t really matter and you can’t justify spending even a little more to get faster performance.  But why limit yourself?  Prices for solid state drives (SSDs) have come down so much over the past couple years making it difficult to justify buying spinning disks, especially the more expensive 15K SAS drives. 

Let’s look at a few examples using our own stock.  Please note that all prices are based on current prices at the time that this blog was published. 

 In the table below, you will see RAID 6 and RAID 10 configurations using 600GB 15K and 900GB 15K drives trying to achieve useable capacity of 4TB or more.  There are many discussions out there about RAID levels for spinning disks.  To avoid getting into them, we have listed RAID 6 and RAID 10.  The two columns on the right show you the extended price (qty * price) and the dollar per usable TB of disk space. 

 

Drive

RAID

Qty

Usable Capacity

Price

Ext Price

$/TB Usable

600GB 15K

6

9

4.2

$259

$2,331

$555

900GB 15K

6

7

4.5

$369

$2,583

$574

 

600GB 15K

10

14

4.2

$259

$3,626

$863

900GB 15K

10

10

4.5

$369

$3,690

$820

 

In the next table, you’ll see the same data using RAID 5 and several of our SATA SSDs.  Compared to the RAID 10 options using 15K drives, you could save up to $1,000 with the Read Intensive (RI) and Mixed Use (MU) SSDs and even get a little more capacity with the 1.6TB MU drives.  You end up with 10x performance at the same or better cost.  Compared to the RAID 6 spinning disks, you may end up having to invest a little more to get the SSDs, but it is a small amount to get 10x performance.  Using the worst-case comparison, the extended prices of the 800GB Write Intensive (WI) SSDs versus the 600GB 15K RAID 6 spinning disks, you end up with a $2,500 additional investment.  If you split that over 3 years (36 months), you spend roughly $70 more per month and you get at least a 10x boost in performance.  There must be a use case in your company to justify spending $70 per month more.  Even if it is just your CEO and CFO can now get their excel files to load faster. 

 

Drive

RAID

Qty

Usable Capacity

Price

Ext Price

$/TB Usable

800GB SATA RI

5

6

4

$449

$2,694

$674

 

800GB SATA MU

5

6

4

$499

$2,994

$749

1.6TB SATA MU

5

4

4.8

$899

$3,596

$749

 

800GB SATA WI

5

7

4.8

$699

$4,893

$1,019

* RI = Read Intensive, MU = Mixed Use, WI = Write Intensive

 

In our last table, we have a comparison using SAS SSDs.  In use cases where you must use SAS drives, like in storage arrays, the investment for SSDs goes up a little but it is completely justifiable when breaking it down to a monthly number.  In the worst-case comparison, the extended prices of the 800GB Write Intensive (WI) SSDs versus the 600GB 15K RAID 6 spinning disks, you end up with a $4,000 additional investment.  Breaking that down over 36 months, gives you a $110 additional investment to get top of the line performing SSDs and 10% more usable capacity.   

 

Drive

RAID

Qty

Usable Capacity

Price

Ext Price

 $/TB Usable

960GB SAS RI

5

6

4.8

 $699

 $4,194

 $874

1.92GB SAS RI

5

4

5.76

 $999

 $3,996

 $694

3.84TB SAS RI

5

3

7.68

 $1699

 $5,097

 $664

 

960GB SAS MU

5

6

4.8

 $999

 $5,994

 $1,249

1.6TB SAS MU

5

4

4.8

 $1,299

 $5,196

 $1,083

1.92TB SAS MU

5

4

5.76

 $1,599

 $6,396

 $1,110

 

400GB SAS WI

5

12

4.4

 $499

 $5,988

 $1,361

800GB SAS WI

5

7

4.8

 $899

 $6,293

 $1,311

* RI = Read Intensive, MU = Mixed Use, WI = Write Intensive

 

All the scenarios above assumed traditional data storage without any data efficiency solutions. In the past, you would see techniques like dedupe and compression used in higher end storage arrays, but the current hyperconverged solutions have taken those same techniques and made them available in their all flash servers.  Considering a low-end dedupe ratio of 1.5x, your pricing would just about be even in most scenarios.  If you are doing something like VDI where you have a lot of duplicate data, your dedupe ratio could be as high as 8x making it multiple times more expensive to use spinning disks.

 

When you break it down into dollars and cents, the case for investing in SSDs makes perfect sense.