3:31 PM
High Technology
Introduction Five years ago we made some predictions about the future development of SSD technology and how it would revolutionize PC storage. Rather than vague musings, we predicted that 2010 was the year SSDs would gain widespread acceptance in the mainstream markets. It turns out we were very close to the mark and things are lining up nicely for a paradigm shift that could have interesting long-term repercussions for a variety of knock-on technologies. SDDs have come a long way in terms of reliability and now are reckoned to be able to last longer than tradional HDDs thanks to wear-leveling algorithms and use a fraction of the power they did in 2005. Even as recently as January 2009, a technology article on Tom's Hardware concluded that SSD performance was not yet good enough - how far things have come in the last year.
This article is primarily a review of Kingston's SSDNow V+ 128GB SSD but, since so few people are really clear about SSDs and even many techies have nagging questions about the technology, we thought we should start off with a technology guide showing how this all came about, the Pros and Cons of SSDs versus traditional HDDs and some Frequently Asked Questions about SSDs. Readers familiar with all this can skip straight to the testing section to see benchmarks but surprisingly, even our hardened techies learnt a thing or two about SSDs while compiling the reference material in the next 3 sections.
It's something that has poor performance characteristics at present compared to the incumbent or mainstream current solution but the rate of improvement (the slope of the line or curve with regards to time) is such that at some point in the future it will overtake the current leading solution. The best way to illustrate this is with the following graph:
Using HDDs as our example we can see (looking forward from 2005, say) that disk speeds are steadily increasing as we move from ATA-33 to ATA-66, ATA-100, ATA-133 to SATA-1, SATA-2 and (unknown to us in 2005) SATA-3). Capacity doubles every year while the price remains constant. Speed has gone up by a factor of 5 in 20 years which is nothing to sniff at but look at what those SSDs are doing! In 2005 they cost a fortune and are slower than HDDs (really only being used by the military and some enterprise solutions where HDDs just couldn't stand the heat) but they sure are improving fast and prices are bound to come down as volumes increase.
Today they are much faster (we shall see during testing just how much faster than the latest HDDs) and more importantly we will examine the difference in practical terms (such as Windows boot times and application loading times) rather than just theoretical speeds in benchmarks. First though, let's take a look at the advantages and disadvantages and then (hopefully) all your SSD questions will be answered in the following section.
- Faster start-up because no spin-up is required.
- Fast random access because there is no read/write head
- Low read latency times for RAM drives. In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law).
- Consistent read performance because physical location of data is irrelevant for SSDs.
- File fragmentation has negligible effect.
- Silent operation due to the lack of moving parts.
- Low capacity flash SSDs have a low power consumption and generate little heat when in use.
- High mechanical reliability, as the lack of moving parts almost eliminates the risk of "mechanical" failure.
- Ability to endure extreme shock, high altitude, vibration and extremes of temperature. This makes SSDs useful for laptops, mobile computers, and devices that operate in extreme conditions (flash).
- For low-capacity SSDs, lower weight and size: although size and weight per unit storage are still better for traditional hard drives, and microdrives allow up to 20 GB storage in a CompactFlash form-factor. Since 2008 SSDs up to 256 GB are lighter than hard drives of the same capacity.
- Flash SSD's have twice the data density of HDD's (so far, with very recent and major developments of improving SSD densities), even up to 1TB disks (currently more than 2TB is atypical even for HDD's)). One example of this advantage is that portable devices such as a smartphone may hold as much as a typical person's desktop PC.
- Failures occur less frequently while writing/erasing data, which means there is a lower chance of irrecoverable data damage.
- Wear leveling used on flash-based SSDs has security implications. For example, encryption of existing unencrypted data on flash-based SSDs cannot be performed securely due to the fact that wear leveling causes new encrypted drive sectors to be written to a physical location different from their original location -- data remains unencrypted in the original physical location. It is also impossible to securely wipe files by overwriting their content on flash-based SSDs.
- As of early-2010, SSDs are still more expensive per gigabyte than hard drives. Whereas a normal flash drive is US$2 per gigabyte, hard drives are around US$0.10 per gigabyte for 3.5", or US$0.20 for 2.5".
- The capacity of SSDs is currently lower than that of hard drives. However, flash SSD capacity is predicted to increase rapidly, with drives of 1 TB already released for enterprise and industrial applications.
- Asymmetric read vs. write performance can cause problems with certain functions where the read and write operations are expected to be completed in a similar timeframe. SSDs currently have a much slower write performance compared to their read performance. (No longer true with newer controllers - Ed)
- Similarly, SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks that are no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks translates into reduced performance.
- Flash-memory drives have limited lifetimes and will often wear out after 1,000,000 to 2,000,000 write cycles (1,000 to 10,000 per cell) for MLC, and up to 5,000,000 write cycles (100,000 per cell) for SLC. Special file systems or firmware designs can mitigate this problem by spreading writes over the entire device, called wear leveling.
- As a result of wear leveling and write combining, the performance of SSDs degrades with use.
- SATA-based SSDs generally exhibit much slower write speeds. As erase blocks on flash-based SSDs generally are quite large (e.g. 0.5 - 1 megabyte), they are far slower than conventional disks during small writes (write amplification effect) and can suffer from write fragmentation. Modern PCIe SSDs however have much faster write speeds than previously available. (Also no longer a problem - Ed)
- DRAM-based SSDs (but not flash-based SSDs) require more power than hard disks, when operating; they still use power when the computer is turned off, while hard disks do not.
- Defragmentation cannot be performed on flash-based SSDs due to wear leveling (operating system cannot control the real physical location of disk sectors). Some SSDs compact free space when idle. However, this improves only writing speed -- not reading speed of existing fragmented data.
This FAQ is a compilation of information we have gathered from around the Internet and will hopefully answer most questions about Solid State Disk technology and help explain some of the technical jargon for newcomers to this field and explain from a practical point of view how SSDs work. Many of the questions and answers relate to SSDs in Windows 7 systems and were originally from Microsoft related discussion groups and forums too numerous to reference here but a Google (or Bing) search using the question as the search term should find the sources if more detail is needed.
Random Reads: A very good story for SSDs
SSDs tend to be very fast for random reads. Most SSDs thoroughly trounce traditionally HDDs because the mechanical work required to position a rotating disk head isn’t required. As a result, the better SSDs can perform 4 KB random reads almost 100 times faster than the typical HDD (about 1/10th of a millisecond per read vs. roughly 10 milliseconds).
Sequential Reads and Writes: Also Good
Sequential read and write operations range between quite good to superb. Because flash chips can be configured in parallel and data spread across the chips, today’s better SSDs can read sequentially at rates greater than 200 MB/s, which is close to double the rate many 7200 RPM drives can deliver. For sequential writes, we see some devices greatly exceeding the rates of typical HDDs, and most SSDs doing fairly well in comparison. In today’s market, there are still considerable differences in sequential write rates between SSDs. Some greatly outperform the typical HDD, others lag by a bit, and a few are poor in comparison.
Random Writes & Flushes: Your mileage will vary greatly
The differences in sequential write rates are interesting to note, but for most users they won’t make for as notable a difference in overall performance as random writes.
What’s a long time for a random write? Well, an average HDD can typically move 4 KB random writes to its spinning media in 7 to 15 milliseconds, which has proven to be largely unacceptable. As a result, most HDDs come with 4, 8 or more megabytes of internal memory and attempt to cache small random writes rather than wait the full 7 to 15 milliseconds. When they do cache a write, they return success to the OS even though the bytes haven’t been moved to the spinning media. We typically see these cached writes completing in a few hundred microseconds (so 10X, 20X or faster than actually writing to spinning media). In looking at millions of disk writes from thousands of telemetry traces, we observe 92% of 4 KB or smaller IOs taking less than 1 millisecond, 80% taking less than 600 microseconds, and an impressive 48% taking less than 200 microseconds. Caching works!
On occasion, we’ll see HDDs struggle with bursts of random writes and flushes. Drives that cache too much for too long and then get caught with too much of a backlog of work to complete when a flush comes along, have proven to be problematic. These flushes and surrounding IOs can have considerably lengthened response times. We’ve seen some devices take a half second to a full second to complete individual IOs and take 10’s of seconds to return to a more consistently responsive state. For the user, this can be awful to endure as responsiveness drops to painful levels. Think of it, the response time for a single I/O can range from 200 microseconds up to a whopping 1,000,000 microseconds (1 second).
When presented with realistic workloads, we see the worst of the SSDs producing very long IO times as well, as much as one half to one full second to complete individual random write and flush requests. This is abysmal for many workloads and can make the entire system feel choppy, unresponsive and sluggish.
Random Writes & Flushes: Why is this so hard?
For many, the notion that a purely electronic SSD can have more trouble with random writes than a traditional HDD seems hard to comprehend at first. After all, SSDs don’t need to seek and position a disk head above a track on a rotating disk, so why would random writes present such a daunting a challenge?
The answer to this takes quite a bit of explaining, Anand’s article admirably covers many of the details. We highly encourage motivated folks to take the time to read it as well as this fine USENIX paper. In an attempt to avoid covering too much of the same material, we’ll just make a handful of points.
- Most SSDs are comprised of flash cells (either SLC or MLC). It is possible to build SSDs out of DRAM. These can be extremely fast, but also very costly and power hungry. Since these are relatively rare, we’ll focus our discussion on the much more popular NAND flash based SSDs. Future SSDs may take advantage of other nonvolatile memory technologies than flash.
- A flash cell is really a trap, a trap for electrons and electrons don’t like to be trapped. Consider this, if placing 100 electrons in a flash cell constitutes a bit value of 0, and fewer means the value is 1, then the controller logic may have to consider 80 to 120 as the acceptable range for a bit value of 0. A range is necessary because some electrons may escape the trap, others may fall into the trap when attempting to fill nearby cells, etc… As a result, some very sophisticated error correction logic is needed to insure data integrity.
- Flash chips tend to be organized in complex arrangements, such as blocks, dies, planes and packages. The size, arrangement, parallelism, wear, interconnects and transfer speed characteristics of which can and do vary greatly.
- Flash cells need to be erased before they can be written. You simply can’t trust that a flash cell has no residual electrons in it before use, so cells need to be erased before filling with electrons. Erasing is done on a large scale. You don’t erase a cell; rather you erase a large block of cells (like 128 KB worth). Erase times are typically long -- a millisecond or more.
- Flash wears out. At some point, a flash cell simply stops working as a trap for electrons. If frequently updated data (e.g., a file system log file) was always stored in the same cells, those cells would wear out more quickly than cells containing read-mostly data. Wear leveling logic is employed by flash controller firmware to spread out writes across a device’s full set of cells. If done properly, most devices will last years under normal desktop/laptop workloads.
- It takes some pretty clever device physicists and some solid engineering to trap electrons at high speed, to do so without errors, and to keep the devices from wearing out unevenly. Not all SSD manufacturers are as far along as others in figuring out how to do this well.
As mentioned above, flash blocks and cells need to be erased before new bytes can be written to them. As a result, newly purchased devices (with all flash blocks pre-erased) can perform notably better at purchase time than after considerable use. While we’ve observed this performance degradation ourselves, we do not consider this to be a show stopper. In fact, except via benchmarking measurements, we don’t expect users to notice the drop during normal use.
Of course, device manufactures and Microsoft want to maintain superior performance characteristics as best we can. One can easily imagine the better SSD manufacturers attempting to overcome the aging issues by pre-erasing blocks so the performance penalty is largely unrealized during normal use, or by maintaining a large enough spare area to store short bursts of writes. SSD drives designed for the enterprise may have as high as 50% of their space reserved in order to provide lengthy periods of high sustained write performance.
In addition to the above, Microsoft and SSD manufacturers are adopting the Trim operation. In Windows 7, if an SSD reports it supports the Trim attribute of the ATA protocol’s Data Set Management command, the NTFS file system will request the ATA driver to issue the new operation to the device when files are deleted and it is safe to erase the SSD pages backing the files. With this information, an SSD can plan to erase the relevant blocks opportunistically (and lazily) in the hope that subsequent writes will not require a blocking erase operation since erased pages are available for reuse.
As an added benefit, the Trim operation can help SSDs reduce wear by eliminating the need for many merge operations to occur. As an example, consider a single 128 KB SSD block that contained a 128 KB file. If the file is deleted and a Trim operation is requested, then the SSD can avoid having to mix bytes from the SSD block with any other bytes that are subsequently written to that block. This reduces wear.
Windows 7 requests the Trim operation for more than just file delete operations. The Trim operation is fully integrated with partition- and volume-level commands like Format and Delete, with file system commands relating to truncate and compression, and with the System Restore (aka Volume Snapshot) feature.
Windows 7 Optimizations and Default Behavior Summary
As noted above, all of today’s SSDs have considerable work to do when presented with disk writes and disk flushes. Windows 7 tends to perform well on today’s SSDs, in part, because they made many engineering changes to reduce the frequency of writes and flushes. This benefits traditional HDDs as well, but is particularly helpful on today’s SSDs.
Windows 7 will disable disk defragmentation on SSD system drives. Because SSDs perform extremely well on random read operations, defragmenting files isn’t helpful enough to warrant the added disk writing defragmentation produces. The FAQ section below has some additional details.
Be default, Windows 7 will disable Superfetch, ReadyBoost, as well as boot and application launch prefetching on SSDs with good random read, random write and flush performance. These technologies were all designed to improve performance on traditional HDDs, where random read performance could easily be a major bottleneck. See the FAQ section below for more details.
Since SSDs tend to perform at their best when the operating system’s partitions are created with the SSD’s alignment needs in mind, all of the partition-creating tools in Windows 7 place newly created partitions with the appropriate alignment.
Frequently Asked Questions
Before addressing some frequently asked questions, we’d like to remind everyone that we believe the future of SSDs in mobile and desktop PCs (as well as enterprise servers) looks very bright to us. SSDs can deliver on the promise of improved performance, more consistent responsiveness, increased battery life, superior ruggedness, quicker startup times, and noise and vibration reductions. With prices steadily dropping and quality on the rise, we expect more and more PCs to be sold with SSDs in place of traditional rotating HDDs. With that in mind, they focused an appropriate amount of their engineering efforts towards insuring Windows 7 users have great experiences on SSDs.
Will Windows 7 support Trim?
Yes. See the above section for details.
Will disk defragmentation be disabled by default on SSDs?
Yes. The automatic scheduling of defragmentation will exclude partitions on devices that declare themselves as SSDs. Additionally, if the system disk has random read performance characteristics above the threshold of 8 MB/sec, then it too will be excluded. The threshold was determined by internal analysis.
The random read threshold test was added to the final product to address the fact that few SSDs on the market today properly identify themselves as SSDs. 8 MB/sec is a relatively conservative rate. While none of their tested HDDs could approach 8 MB/sec, all of their tested SSDs exceeded that threshold. SSD performance ranged between 11 MB/sec and 130 MB/sec. Of the 182 HDDs tested, only 6 configurations managed to exceed 2 MB/sec on our random read test. The other 176 ranged between 0.8 MB/sec and 1.6 MB/sec.
Will Superfetch be disabled on SSDs?
Yes, for most systems with SSDs.
If the system disk is an SSD, and the SSD performs adequately on random reads and doesn’t have glaring performance issues with random writes or flushes, then Superfetch, boot prefetching, application launch prefetching, ReadyBoost and ReadDrive will all be disabled.
Initially, we had configured all of these features to be off on all SSDs, but we encountered sizable performance regressions on some systems. In root causing those regressions, we found that some first generation SSDs had severe enough random write and flush problems that ultimately lead to disk reads being blocked for long periods of time. With Superfetch and other prefetching re-enabled, performance on key scenarios was markedly improved.
Is NTFS Compression of Files and Directories recommended on SSDs?
Compressing files help save space, but the effort of compressing and decompressing requires extra CPU cycles and therefore power on mobile systems. That said, for infrequently modified directories and files, compression is a fine way to conserve valuable SSD space and can be a good tradeoff if space is truly a premium.
We do not, however, recommend compressing files or directories that will be written to with great frequency. Your Documents directory and files are likely to be fine, but temporary internet directories or mail folder directories aren’t such a good idea because they get large number of file writes in bursts.
Does the Windows Search Indexer operate differently on SSDs?
No.
Is Bitlocker’s encryption process optimized to work on SSDs?
Yes, on NTFS. When Bitlocker is first configured on a partition, the entire partition is read, encrypted and written back out. As this is done, the NTFS file system will issue Trim commands to help the SSD optimize its behavior.
We do encourage users concerned about their data privacy and protection to enable Bitlocker on their drives, including SSDs.
Does Media Center do anything special when configured on SSDs?
No. While SSDs do have advantages over traditional HDDs, SSDs are more costly per GB than their HDD counterparts. For most users, a HDD optimized for media recording is a better choice, as media recording and playback workloads are largely sequential in nature.
Does Write Caching make sense on SSDs and does Windows 7 do anything special if an SSD supports write caching?
Some SSD manufacturers including RAM in their devices for more than just their control logic; they are mimicking the behavior of traditional disks by caching writes, and possibly reads. For devices that do cache writes in volatile memory, Windows 7 expects flush commands and write-ordering to be preserved to at least the same degree as traditional rotating disks. Additionally, Windows 7 expects user settings that disable write caching to be honored by write caching SSDs just as they are on traditional disks.
Do RAID configurations make sense with SSDs?
Yes. The reliability and performance benefits one can obtain via HDD RAID configurations can be had with SSD RAID configurations. (Please note - SSD RAID Arrays cannot user TRIM at present even if each drive alone can)
Should the pagefile be placed on SSDs?
Yes. Most pagefile operations are small random reads or larger sequential writes, both of which are types of operations that SSDs handle well.
In looking at telemetry data from thousands of traces and focusing on pagefile reads and writes, we find that
- Pagefile.sys reads outnumber pagefile.sys writes by about 40 to 1,
- Pagefile.sys read sizes are typically quite small, with 67% less than or equal to 4 KB, and 88% less than 16 KB.
- Pagefile.sys writes are relatively large, with 62% greater than or equal to 128 KB and 45% being exactly 1 MB in size.
Are there any concerns regarding the Hibernate file and SSDs?
No, hiberfile.sys is written to and read from sequentially and in large chunks, and thus can be placed on either HDDs or SSDs.
What Windows Experience Index changes were made to address SSD performance characteristics?
In Windows 7, there are new random read, random write and flush assessments. Better SSDs can score above 6.5 all the way to 7.9. To be included in that range, an SSD has to have outstanding random read rates and be resilient to flush and random write workloads.
In the Beta timeframe of Windows 7, there was a capping of scores at 1.9, 2.9 or the like if a disk (SSD or HDD) didn’t perform adequately when confronted with their random write and flush assessments. Feedback on this was fairly consistent, with most feeling the level of capping to be excessive. As a result, they now simply restrict SSDs with performance issues from joining the newly added 6.0+ and 7.0+ ranges. SSDs that are not solid performers across all assessments effectively get scored in a manner similar to what they would have been in Windows Vista, gaining no Win7 boost for great random read performance.
Finally we can move on to the main focus of this review which is Kingston's SSDNow V+ 128GB Performance ATA-2 Solid State Disk.
Features
- Innovative — Uses MLC NAND flash memory components.
- Silent — Runs silent and cool with no moving mechanical parts.
- Shock Proof — No moving mechanical parts so the SSD handles rougher conditions.
- Supports S.M.A.R.T. — Self-Monitoring, Analysis and Reporting Technology to help maintain a healthy drive
- Guaranteed — 3 year legendary Kingston warranty, 24/7 tech support
- Sequential Read Throughput — 230MB/s
- Sequential Write Throughput — 180MB/s
- Form Factor — 2.5"
- Interface — SATA 1.5 Gb/sec. and 3.0 Gb/sec
- Capacity1 — 64 GB, 128 GB, 256 GB, 512 GB
- Storage temperatures — -40 - 85°C
- Operating temperatures — 0 - 70°C
- Dimensions — 69.85 x 100 x 9.5 mm
- Weight — 84 gram
- PCMARK® HDD 2005 Score 2 — 64 GB — 38,177
128 GB — 38,065
256 GB — 38,272
512 GB — 37,974
- Vibration operating — 2.17G
- Vibration non-operating — 20G
- Power specs — 2.6 W - active / 0.15W Idle
- Life expectancy 2 — 1,000,000 Hrs mean time before failure
- Operating shock — 1500G
2 Based on internal testing. Performance may vary based on system settings
Test Configuration | ||
System Hardware | ||
CPU | Intel Core i7-870 (2.93 GHz, 8MB Cache | AMD Athlon 2 X4 630 (2.8 GHz, 2MB Cache) |
| Motherboard | ASUS Maximus III Gene | ASUS M4A79T Deluxe |
| CPU Cooler | Corsair H50 | Corsair H50 |
| RAM | Kingston KHX2133C8D3T1K2/4GX 4GB 2133MHz DDR3 Non-ECC CL8 (Kit of 2) Intel XMP Tall HS CAS 8-8-8-24 | Kingston KHX1600C8D3T1K2/4GX 4GB 1600MHz DDR3 T1 Series Non-ECC CL8 DIMM (Kit of 2) XMP CAS 8-8-8-24 |
| Graphics | ATI Radeon 5850 HD | ATI Radeon 5850 HD |
| Hard Drive |
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| Sound | SupremeFX X-Fi built-in | Realtek® 1200 8 -Channel High Definition Audio CODEC |
| Network | Gigabit LAN controller | Realtek® 8112 Gigabit LAN controller |
| Chassis | Antec 902 Midi Tower Case | Antec P183 Ultra Quiet Case |
| Power | Antec TruPower 750W | Antec CP-1000 750W |
Software | ||
| Operating System | Windows 7 Professional | Windows 7 Professional |
| Graphics | ATI Catalyst 9.11 | ATI Catalyst 9.11 |
| Chipset | Intel P55 | AMD 790 |
| Applications |
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HD Tune Pro 3.5 is our standard benchmark for storage devices and has served us well since we moved from HD-Tach. It allows comprehensive read and write tests that stress both SSD and HDDs as well as optical and flash drives.
AS SSD is a benchmark designed exclusively for SSDs but handles HDDs just as well. It also gives a nice graphical summary of results so readers don't have to look at boring derived Excel charts.
Everest is a very comprehensive benchmarking suite that covers all aspects of system performance in much the same was as SiSoft Sandra does. Here we are using the Storage tests.
We knew that the Kingston V+ 128GB SSD was going to beat the Samsung 1TB HDD but would it be enough to justify double the price and almost 40 times the cost per Gigabyte? In our opinion, the answer is most definitely yes, not because of the benchmarks but rather the experience of using an SSD instead of HDD and having Windows 7 boot up in less than half the time and even more, seeing games and applications load in the blink of an eye because SSDs can be a hundred times faster than HDDs when loading numerous small files.
SSDs have a long way to go before being cheaper than HDDs in terms of cost per GB but this should not put people off purchasing as the best combination today is an SSD as the boot drive containing the Operating System and a conventional HDD of whatever size is needed for storage/archiving data that is less frequently accessed.
Kingston have really been a key player in pushing forward the adoption of SSDs, partly because of their background in memory manufacturing but also in an effort to drive innovation - something which has seen them recently announce record revenues during a time of recession. Intel may have led the way with their X-25M SSD but have rested on their laurels to allow others like Kingston to take the price and performance lead. Next week we will be taking a look at Kingston's V series SSD drive which is aimed at the entry level consumer and priced at below £100 and we will see what performance is like at the budget end of the SSD market.
For now the only competitors able to beat Kingston's V+ in terms of performance are the top end drives from Intel and OCZ etc. which are only slightly faster in benchmarks (not at all noticeably faster in real world experience) and cost twice as much. That makes the Kingston SSDNow V+ series of SSD drives the obvious choice for a performance SSD purchase.
