Solid State Disks under the spotlight

I’ve looked at the idea of using SSD – Solid State Disk – in the storage column before but it is an idea that seems to be rapidly moving into the mainstream rather than being a specialist option.

When I last looked at SSD, my conclusion was that this could be the year that solid state storage really comes into its own, and that this low-power, quiet and cheap storage medium might finally give mechanical hard disks a run for their money.

I've recently been trying out some SSDs from Kingston Technology that back up this idea. Kingston Technology has two lines of reasonably priced SATA SSDs and they are both drop-in replacements for standard 2.5inch SATA drives.

The SSDnow M series is aimed at workstations and the SSDnow E series is aimed at servers, although I suspect that the E series might be useful for a wider range of applications. The E series is based on Single Level Cell SLC technology, which is faster than the usual Multi Level Cell MLC technology used in the M series, and both are essentially Intel products rebranded.

Both models offer the high read rates typical of Flash memory, i.e. 250MBytes/s, but the E series writes at 170MBytes/s compared with the (still respectable) 70MBytes/s offered by the M series. What's more, these speeds are more or less realised in practice. To put these figures in context a hard drive (2.5 inch) manages around the 50MByte/s mark.

All of the SSDnow drives are packaged in the same way and are identical in form factor and fitting to standard 2.5inch drives. They also have standard SATA sockets and can be simply regarded and treated as if they were 2.5 inch SATA drives that just happen not to have any moving parts.

The drives are also very low power, with the E series consuming 2.4W while active and a negligible 0.06W in sleep mode. The M series is even lighter on power, consuming 1.5W when active and 0.06W in sleep mode. To put these figures in context, the E series is just a little more efficient than the best 2.5 inch drive and the M series uses about half the power – clearly this is one reason for preferring the M series in a portable application. Compared to a full-sized 3.5 inch drive the power consumption of either drive is less than a quarter.

As a simple test I installed a desktop operating system on a 32Gbyte E series drive in a fairly standard server. Installation of the drive was indistinguishable from the task of installing a standard 2.5 inch drive, and this makes either the E or M series a drop-in replacement for the drive in any portable. Operating installation was noticeably faster and once complete the system booted and worked perfectly. The only really noticeable difference was the liveliness of the machine – it was reborn.

Simple timings of application loading and other tasks suggested that things were working about four times faster but the psychological impact seemed greater, perhaps due to the lower latency effect. More precise testing confirmed the manufacturer’s data transfer rates within the usual margins.

Put simply, the SSDnow drives from Kingston seem to deliver the goods promised by SSD – they are faster, totally silent, and with no moving parts effectively immune to shock and vibration. The quoted mean time to failure is 2 million hours (E series) and low write current and wear-leveling is used to achieve this long lifetime. The drives also include a large (~20GBytes) of hidden memory that can be used to replace failed storage cells and to be used in the wear-levelling algorithm.

The E series is currently available in 64 and 32GByte configurations and the M series is available in 80 and 160GBytes. Again the larger capacity in the M series makes it especially suited to use in a portable. However, my guess is that the speed increase offered by the E series will see these drives also used in the “ultimate” portable configuration.

The only downside of the SSDnow series, both the E and the M series is cost. The 32GByte E series cost about £500 which translates to £15 per GByte. The M series costs about £400 for the 80GByte drive which translates to £5 per GByte. These figures have to be compared to a typical £0.06 per GByte for a 3.5 inch and £0.20 per GByte for a 2.5 inch drive.

Clearly you aren’t going to replace a standard hard drive by an SSDnow drive unless you really need the speed, robustness or the silence they offer. However, if you defray the cost over their longer life span they work out as a more reasonable proposition and once the purchase price reduces over time then these drives have a much wider appeal.

Kingston Technology