Rethinking Storage for Microservers Page 2 - Page 2


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With the flexibility that microservers offer, considering multiple storage layers is important. Let's start by examining local storage to see what a single server has available.

Local Storage

Let's assume our microserver has a single hard drive attached. These are almost always 2.5" SATA drives. Since price is something of an objective for microservers, I will focus on consumer-type drives. This also gives an idea of the lowest price per GB and the minimum overall price. These numbers can also serve as guideposts for where enterprise storage may be in the not too distant future. For pricing I'll just use a favorite of mine, Newegg.

At one end of the storage spectrum is capacity. The largest capacity 2.5" laptop drive I could fine is a 2 TB, 2.5" SATA drive for about $180.00 (as of the writing of this article). It's probably not the fastest drive (uses Western Digital's "IntelliPower" which appears to mean that it has a fairly low rotational speed — perhaps 5,000 - 5,900 rpm), and it only has an 8MB cache on a 3 Gbps SATA interface. But in this case, we're only after capacity, so I'm not too worried about the drive interface and the cache size. This drive gives a large capacity at $0.09/GB (pretty inexpensive). But remember that it is a consumer drive, so don't think that you can get this price point in an enterprise drive.

At the opposite end of the storage spectrum is performance. The best performance we'll get for a single drive is obviously an SSD. However, we still need a reasonable capacity, so let's look for large capacity SSD drives. There is a 1 TB SSD that is a bit expensive at around $2,500. But there is a more reasonable 512GB SSD for about $380.00. Let's focus on the lower capacity drive since it has a better price per GB ($0.74/GB) than the larger drive. It has good performance since it has a SATAII interface (6 Gbps) with about 500 MB/s for sequential reads, 260 MB/s for sequential writes, up to 45,000 random read IOPS, and up to 50,000 random write IOPS.

The large capacity disk and the large capacity SSD bracket the performance and capacity options for a microserver with a single drive. The spinning drive has tons of capacity, but it is likely to have fairly low performance — 100MB/s or less with very low IOPS relative to SSDs. But it has a very attractive price per GB and only costs about $180.00.

The SSD has much greater performance, particularly for random IOPS, but costs a bit more ($380.00) and the price per GB is about 8 times more than the spinning drive.

One key thing to keep in mind is that microservers are fairly inexpensive, with list prices currently about $750 per server without a drive. The spinning drive is about 24 percent of the price of the server, but the SSD is about 50 percent the price. Do you buy a lower-cost, high-capacity drive with poor performance or an SSD with less capacity, much higher performance, and a higher cost?

One option to improve this situation is to perhaps rethink local storage in microservers. At this time, each server basically gets one 2.5" disk or SSD for local storage. However, there is an interface called mSATA or mini-SATA that is becoming popular for small SSDS in netbooks and laptops. An example of an mSATA SSD drive is the Intel 525.

Some of these drives, such as the Intel 525 240GB mSATA drive, can have really amazing performance. The specs on the drive indicate a maximum sequential read performance of 550 MB/s, a maximum sequential write performance of 520 MB/s, a 4KB random read IOPS of up to 80,000, and a 4KB random write IOPS of up to 50,000. mSATA SSD drives can also be up to 480GB in capacity. At this time, the pricing on these consumer drives is a little more than $1.00/GB at this scale.

Imagine being able to put two to four of these mSATA drives on each microserver using either a simple RAID controller on the SoC or software RAID. Then you might be able to get well over 1 GB/s in performance with lots of IOPS. However, the capacity won't be that large and the price per server will be higher than you might want.

While an interesting idea, mSATA SSD drives don't get us out of the pickle of needing larger capacity storage and better price/performance. My opinion is that we'll need network storage for this situation, and we'll definitely need it for diskless servers.

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