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Thread: Tech Demystified - SSD is now a mainstream replacement for Hard Drive

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    Administrator M.A.A's Avatar
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    Tech Demystified - SSD is now a mainstream replacement for Hard Drive

    SSD came along using solid-state technology, to perform three, four or five times faster. As well as speed, SSD technology has a number of other critical advantages in respect of performance. And if it hadn't cost a proverbial arm and leg plus torso, we'd have all ditched spinning metal discs some while back.

    Prices are now more approachable, but the technology has some unexpected twists, which I'll now try to provide some guidance on for those who are interested in buying and using solid-state storage.

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    The SSD Recipe
    At this point, all SSDs, whatever brand or make, conform to a basic model of how they're constructed and what they deliver. They mostly use NAND flash memory modules, usually driven by an ARM based controller and connected to the PC by a SATA interface.

    There are some exceptions to this profile, in respect of how NAND memory is organized, one being multi-level cell (MLC) and the other being single-level cell (SLC)flash memory. In general, SLC is seen to be less reliable in the long term, though module interleaving and wear-levelling algorithms can address this aspect. SATA also isn't exclusively employed. You can get SSDs that connect directly to the PCI Express bus on a card, use SATA variation like mSATA or enhanced server technologies like Fiber Channel and SAS (Serial Attached SCSI).

    Whatever the design, an SDD can be assessed by a combination of four factors: performance, endurance, cost and capacity. These are the criteria on which an SSD need to be judged, because it's just not possible to have the best of all these worlds in a single unit.

    The highest performing drives or the ones with the greatest capacities aren't cheap and, equally, high endurance isn't to be expected from a budget drive. Those points made, there are some sweet spots to be had between the cheap, low capacity models and those with true solid-state performance.

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    Understanding Endurance

    For many reasons, mostly their misuse, a big question mark is always placed over the long-term reliability of SSD drives. Flash memory has a limited number of program-erase (PIE) cycles before integrity of the data stored on the device is called into question. A good memory modules might reasonably expect a million operations, but the way that NAND memory works often means that bit locations that are unaffected by a data change are also altered, as the entire block is erased and rewritten. To reduce the effect of certain areas of the SSD wearing out before the rest, most designs now incorporate wear-levelling code that keeps a check on the usage and spreads operations around.

    Makers usually quote the reliability of the drive in TBW or total bytes written. Intel's X25 drives, for example, claim a TBW of five years, with 20GB being written each and every day. That works out as roughly 36TB of total writes, before the drive is done. The problem with that information is that most of us have no idea how much data we typically write to our system drive on a daily basis or where in the greater scheme of its life we are. It's entirely possible that you only write a couple of gigabytes per day and your SSD would go on for decades or that you're editing video files where you shift a terabyte of data through the system, reducing life dramatically.

    What's also a big influence in these calculations is surely how big the drive is, because a 1TB drive would only, in theory, have each cell rewritten once a day even if you wrote 1TB of data to it. This more than hints that larger drives will last longer purely from the amount of data traffic each part of the drive will see.

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    Research reveals that most users write less than 5GB/s per day, and those that write more than 50GB/s are less than 1% of the user base. Based on those numbers, most users would only rewrite the entire contents of their 250GB drive every 50 days, and only seven times each year. Death, at this speed, would come very slowly.In short, unless you absolutely hammer your system, expect it to go on indefinitely, and unless you have an SSD with a manufacturing fault, you're unlikely to experience the sort of failure that most people are worried about.

    It would help if drive makers could design some sort of usage gauge, so you could assess where your SSD was, but this problem might soon go away entirely. In 2012, Taiwanese flash expert Macronix revealed a design for self-healing NAND modules that use annealing to erase and repair cells. These promise to push typical lifespans to 100 million cycles, a level where even the heaviest users would have problems exhausting the life of a module. When these eventually come to market, the talking about SSD lifespan will end.

    Understanding Performance

    There's a real problem with SSD marketing, because they're often promoted purely on the basis of MB/s in terms of reading and writing. While that's important, especially if you move large files around, it's not the whole story.

    As well as speed, SSD technology has a number of other critical advantages in respect of performance when compared with a conventional disk storage medium. One of these is that an SSD can access random locations just as rapidly as sequential ones, which is why fragmentation on this technology is meaningless.

    The other advantage is its ability to consume many thousands of different requests for reading and writing per second and treat them all with the same contempt.
    The unit of measurement that's important here is IOPS (input output operations per second), and how good an SSD is at this is often a better indicator of potential performance than how rapidly it reads or writes large files.

    Normally IOPs are defined by the block sizes, and most SSDs are organized into 4K sectors, for optimal running. High IOPS are linked to MB/s, and there's a calculation where you can work out each from the other, but there's also additional details about how many simultaneous threads a controller can work with in the operational queue.

    The true test of IOPS comes when the SSD is used in a server or on a desktop system where the multitasking is being heavily utilized. In general, PC usage IOPS might not be critical, but they are a good indicator of the overall quality of the module and what performance is likely to be like.

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    Understanding Capacity
    Surely size is whatever memory capacity the module contains and there's nothing more to understand to it than that? I wish that was true, but the capacity of an SSD can have rather odd implications for its performance.Let's take a typical consumer drive, the Plextor PX-M5S Series, and see what performance you can expect from it. Well, the Plextor promotional material talks about sequential reads of up to 520MB/s. But anyone who has suffered with less than promised broadband speeds will be wary of the expression 'up to'.

    However, the following chart better reveals how the size of a SSD, due to the organizations of the modules can dramatically impact on performance, most notably in respect of write speed and write IOPS.However, the capacity doesn't only influence the overall write/read performance. It also impacts on the TBW, though I couldn't find an actual TBW quoted for these devices. They're given a MTBF of 1.5 million hours, but that's not very informative about PIE operations.

    The simple answer is that if you're concerned about SSD life or want the best performance, then go for bigger drives, as they win on both fronts.

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    Moderator Lienia henna's Avatar
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    The SSD is undoubtedly the best upgrade you can implement

    The SSD is undoubtedly the best upgrade you can implement, I've used a combination of SSD and conventional hard drive for a couple of years now, and it's certainly the best combination. Maybe in another five years we'd do away entirely with disk based magnetic storage, though the capacities available then might keep it as the most cost effective way to manage large data collections.

    As for the humble SSD, it's likely to get larger, faster and ultimately alter the idea that booting a device should involve some waiting. It's likely that the SATA interface will evolve with the SSD to provide the same sort of bandwidth that RAM currently enjoys, as the difference between workspace memory and non-volatile storage breaks down.

    That development could usher in the biggest change in PC architecture since the IBM XT. In the meantime, the SSD is getting cheaper, faster and more reliable, and soon all new computers will come with one from the outset. What's great about them from an enthusiast viewpoint is that you can drop them into a system running Windows 7 or 8 or Linux, like they're a conventional hard drive. Transferring to them is exactly the same as moving to another hard drive, and most modern operating systems are 'SSD aware' once you're using them.

    If you want to see very immediate improvements in booting your PC and launching, applications, then the SSD is undoubtedly the best upgrade you can implement. As with all things, there can be caveats, with many people citing concern over long-term reliability as the reason they've stuck with conventional storage. But unless you run your PC 24/seven for years on end, you're probably no more likely to encounter these issues then you are to have a hard drive fail spontaneously.

    The only significant blot on this John Constable painted landscape is the cost per gigabyte, though we've seen dramatic falls in that over the past couple of years. Prices are now at a level where a 128GB SSD device is certainly within the budget of many PC owners, and that's sufficient space to work with alongside a conventional drive in a desktop Pc.
    For mobile computing users the choice is less obvious, as many laptops only have the space for a single drive. A drop in capacity from 1TB to 128GB might be unrealistic, depending how much data you generally carry with you. But if you do convert to SSD you'll generally get the bonus of extended battery life for paying a space penalty.

    Many Ultra book models are now coming with an SSD as standard, demonstrating the now unstoppable movement away from physical drives in the mobile space. Those changes and the massive growth in SSD sales tell only one story: the future of storage is SSD, and it's here now.

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    Member B.Ali's Avatar
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    Solid State Sustainability

    I've read how much praise solid state drives get in pretty much all areas. I have also read (somewhere online) that the number of write cycles to the SSD is finite, and eventually it will stop working. Some reports suggest 10 or so years of average computer use will see the end of an SSD.


    I've had mechanical hard drives celebrate their 15th birthday and they're still going strongly, which begs the question: what happens when an SSD begins to run out of write cycles? Will all data be lost? Some of it wiped? Or am I worrying over nothing and been misinformed?


    We know the short term benefits of these SSDs, however there is very little information on this area to research and I'd appreciate your feedback on the use of these SSDs long term.

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    Administrator M.A.A's Avatar
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    Hello, Ali.
    Solid state technology is now far more prevalent, there's still a lot of confusion over it, especially when it comes to the durability and lifetime of the media. As with any technology, solid state has all sorts of pros and cons, with the most important being performance, cost, and (of course) durability. Solid state is a far better performer than traditional hard disk tech, with less latency and faster data transfer speeds. It's also more energy efficient due to having no moving parts, and this also means a potential major drop in the instances of failure.

    Sadly, though, solid state is still far more expensive that older magnetic platter tech, and the ratio of sterling pounds to gigabytes is still unacceptable for many. SSD drives are expensive if you want plentiful storage. This means that most of us choose to stick with the more affordable, and larger capacity mechanical hard disks.
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    However, if you want a speedy and quiet system, SSD is the way to go, which leaves us with the durability issue. As you've said, SSD tech does have a limited lifetime, with a finite number of writes per memory cell. As the technology has dropped in price due to less expensive materials and production methods being used to create SSD drives, this lifetime has shortened even more. Lifetime of an SSD cell varies with make, model and memory cell type, but a rough guide to this is as follows:
    TLCNAND flash (Triple-Layer Cell): c. 1K cycles
    MLC NAND flash (Multi-Layer Cell) c.5-10K cycles
    SLCNAND flash (Single-Layer Cell) c. 100K cycles
    Obviously, it's the TLC technology that is used at the cheaper end of the SSD market, so these drives don't last as long, with SLC being the most durable. However, MLC is by far the most prevalent consumer SSD type (though TLC is, technically speaking, also MLC), and SLC is the most expensive, often used in enterprise environments where longer lifetimes are absolutely critical.

    So what does this mean for the average consumer? Well, to be perfectly honest, not that much. SSD drives do have limits, sure, but these limits, even on a TLC NAND device, are not as bad as you may think. Each NAND cell in the SSD device has a lifetime, not the whole unit as one, and data can be shifted from one cell to another as is needed, so if a cell suffers a failure (which it will when the write limit is met), data can be shunted to another cell. The larger the volume, the more cells you have, and so the longer it'll last, even if the individual cells are less durable.

    That said, MLC is the best form to go for, as the tech is faster as well as more durable, and in turn, more economical. Typical daily use means that most MLC cells will probably last 20+ years (that's copying around 5GB of data per day), comparable, and actually better than a lot of magnetic disks, and that's without the mechanical failures normal hard drives are vulnerable to, making 550 a great option, even against the usually no degradable magnetic platter of the HDD.
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    One issue users should be aware of is SSD's reported vulnerability to power outages. Although it's by no means a rock solid occurrence, it's been known for SSD drive to drastically fail after power outages, and many simply cannot survive multiple such outages. This may be a big issue for those living in areas with regular brown- or blackouts, or even if a system is unplugged accidentally or crashes. Of course, these incidents are still rare, but it can happen, so is worth bearing in mind.

    SSD performance is also affected by the amount of data on the unit. The more data on the drive there is, the lower the performance. As the cells fill up, data access speeds can drop, and although technology like TRIM can help alleviate this, it's a real issue, so SSD users should always keep their data storage in check. SSD lifetime can be extended if users install more RAM into their systems, too. Various sites and publications have tested this, and more RAM (which can hold more data) can reduce the number of writes needed per NAND cell, thus extending the lifetime of an SSD unit.

    With all of these pros and cons, and the tricks needed to get the most out of SSD, you'd be forgiven for sitting on the fence pondering whether to jump from the overgrown garden of magnetic drives into the new, well-trimmed lushness of SSD's back yard. If this is the case, there may be a better option to help persuade you, and that's hybrid drives.

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    Hybrid drives mix both magnetic platters and SSD cells to create a fusion of the technologies. Magnetic platters are used to store the data, and the SSD cells are used to store the most commonly used information for faster access. This eliminates a lot of the issues with write limitations whilst granting users increased data access speeds. Sadly, it also reintroduces the delicate nature of magnetic platters, and writing or accessing new data on the unit is done so at normal HDD speeds (it's not cached until re-read from the drive itself), but if you're already using standard hard disks, this isn't such a bad thing.

    Luckily, hybrid drives only require a small amount of SSD to greatly boost the data access speeds of a magnetic drive, and so the cost of hybrids is far more approachable than pure SSD units. Even large 2TB hybrid models can cost less than 100. Compare that with some 1TB SDD units that can cost around 500, and you've got quite a difference.

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    Everyone loves a new storage device and Crucial has unveiled the M550 SSD, a drive developed by parent company Micron that's compatible with both PC and Mac systems and comes backed with a three-year warranty.
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    Designed to meet our ever-expanding digital desires, the M550 SSD offers 20-times higher performance than a traditional hard drive and also gobbles up less power while doing so. With quick boot-up, fast file and program access, plus near-instant wake from sleep, it all shapes up to a higher performance drive in general.

    With sequential speeds reaching up to 550MB/s for read and 500MB/s write, this promises to have maxed out the SATA 6Gb/s capabilities and the advanced feature set includes data protection in the form of on-board power-loss protection and advanced error recovery techniques for any mishaps. Offered up in 128GB, 256GB, 512GB and 1TB capacities.

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    hi everyone
    The hard drive in my laptop died recently and to replace it I've ordered a 240GB SSD. When it arrives I'll need to reinstall Windows 7, but I believe partitions on SSDs have to be set up differently to those on traditional drives (spinners). How do I go about doing this? This is my first SSD. I've looked online but just got lost amongst all the jargon.

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    Administrator M.A.A's Avatar
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    What you're perhaps concerned about is alignment. Pre-Vista versions of Windows align partitions on 512-byte boundaries, as hard drives have traditionally been divided into 512-byte sectors. However, all SSDs and many modern spinners (especially those with 2TB+ capacities) are divided into 4,096-byte sectors, so partitions on these need to be aligned to 4,096-byte boundaries.

    Misalignment saps performance and can even shorten an SSD's life (it causes extra write and erase cycles to the cells). You don't need to worry though, Robert as you'll be installing Windows 7. With this, and also with Vista and Windows 8.x, all partitions on SSDs and spinners alike - are aligned to 4,096-byte boundaries as standard. As 4,096 is divisible by 512, even drives with 512-byte sectors are fine and dandy with that.

    For users installing Xp, it would be a different story it could also be different for users installing a later Windows version to a partition that's been created manually - that is, a partition not set up by the OS's own installation wizard. That happens a lot when users are migrating a cloned backup.

    Checking alignment and realigning if required, is now very easy to do. Don't worry about having to wipe the SSD and start again or any nonsense like that. Head here and grab a copy of the marvelous MiniTool Partition Wizard:. This'll handle it all for you. And it's free!

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