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Nowadays everyone has windows and softwares installed on a ssd. But most people still have HDDs for their personnal data (movies, music, work related data etc), usually on large hdds (1to and more).

Price of ssds is still quite high, 1to costs roughly 300€ where a similar sized hdd costs 80€.

Still, price aside, is it a good idea to replace this data drive with a ssd ? I think its a lot harder to retrieve data if the ssd fails. Also I fear the continuous use of the ssd (write) might lower its life span.

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Still, price aside, is it a good idea to replace this data drive with a ssd?

Whether it is "a good idea" is largely subjective, but there are some workloads that can benefit from the additional I/O speed of a SSD compared to a rotational HDD. Particularly, any seek-heavy workload will be helped by the SSD's much greater IOPS capability ("seek speed"; IOPS is I/O Operations Per Second). Rotational HDDs can do on the order of 100 IOPS, whereas many SSDs can do 10,000 to 100,000 IOPS. That is a massive difference and the reason why SSDs are so much faster in such workloads. System startup is usually very seek-intensive, which is why systems where the HDD is replaced by a SSD (even without making any other changes) often see a significant improvement in boot time.

Opening a single document is likely to be more CPU-bound than I/O-bound (and certainly seek-latency-bound), so will not show any major difference unless both the particular software you are working with and your operating system is grossly inefficient at caching.

Rotational HDDs are usually "good enough" at sequential I/O, which means that any largely sequential workload, such as streaming through a single large file from start to finish without significant seeking, won't see any significant improvement from being moved to a SSD. Most rotational HDDs can do 100 MB/s or more in sequential workloads, which is plenty good enough for almost anything you will encounter on a personal/home system. For comparison, high-quality compressed video is often on the order of perhaps 1 MB/s data rate.

SSDs do have a few other, potentially fairly significant, advantages that should not be dismissed:

  • Reduced power usage (which leads to less heat dissipated, which means slightly less need for cooling); rotational HDDs draw about 5-10 W, an idle SSD might draw as little as a few tens of milliwatts, and it's rare that any draw more than about half a watt even in active use.
  • Less noise, both from the reduced need for cooling as well as because the SSD itself (unlike a rotational HDD) has no moving parts.
  • Less susceptible to damage due to physical movement. This is especially useful in a laptop or other device that is used on the go, but can be a benefit in desktop installations as well.

Wikipedia has a more complete list comparing characteristics of SSDs and rotational HDDs, including startup time, access latency time, reliability, temperature, noise, and more.

I think its a lot harder to retrieve data if the ssd fails.

It's good that you are planning ahead, but this is better solved by having a solid backup regimen in place, than by thinking about recovering data from a broken drive. Data recovery from a broken drive should be a last-ditch resort, not something you consider normally.

If you are really worried, set up a RAID 1 (mirror) with a second drive. RAID is not a backup but it will significantly reduce the risk for downtime in case of drive failure. However, modern SSDs are reliable enough that this should not be a major concern in daily use (also see below).

Also I fear the continuous use of the ssd (write) might lower its life span.

With modern SSDs and personal-type workloads, not to the point that it matters. Even in server workloads, these days, properly spec'd SSDs are generally considered reliable enough for most uses, and server workloads tend to be significantly heavier than any personal/home type workload.

If you are really worried, look up the spec sheets for the specific model SSDs you are interested in; if the drive is good, those will state workload figures like "X GB per day for Y years" for which the drive is expected to remain fully functional. You will most likely find those figures far larger than what your needs are.

You may also want to read through The SSD Endurance Experiment. Particularly, while noting that the specific models may or may not be available any longer (and this is not an endorsement for or recommendation against any particular vendor or product), the introduction to that specific page states that:

Our SSD Endurance Experiment has left four casualties in its wake so far. Representatives from the Corsair Neutron Series GTX, Intel 335 Series, Kingston HyperX 3K, and Samsung 840 Series all perished to satisfy our curiosity. Each one absorbed far more damage than its official endurance specification promised—and far more than the vast majority of users are likely to inflict.

The last victim fell at 1.2PB, which is barely a speck in the rear-view mirror for our remaining subjects. The 840 Pro and a second HyperX 3K have now reached two freaking petabytes of writes. To put that figure into perspective, the SSDs in my main desktop have logged less than two terabytes of writes over the past couple years. At this rate, it'll take me a thousand years to reach that total.

For practical personal workstation workloads and with modern SSDs, flash failure due to wear will not be what causes the drive to fail. Flash failure is also something that the firmware on the drive can predict, and thus can be estimated when it will happen with a fairly large degree of certainty. Set up SMART monitoring on the drive and you won't have to worry about that; the system will notify you when the drive is nearing what the manufacturer feels is its reliability threshold, and you can replace it proactively at that point.

SSDs failing very soon after they are brought into service (like some of the horror stories of early SSDs that would fail within days to months) is more likely to have causes other than flash failure, and will be covered by the manufacturer's warranty in any case. As long as you have backups, that will be an annoyance, but not really anything much more than that.

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@Michael Kjörling has a very good, thorough answer, but I think I'll post here also since I have some info on the data recovery aspect.

"Nowadays everyone has windows and softwares installed on a ssd. But most people still have HDDs for their personnal data"

I think nowadays most people still just have one drive, but yes, that is much more common lately. All of my current desktop computers have an SSD for OS/programs and a spinning hard disk for data like you say. I have definitely noticed the improvement.

"Is it a good idea" to replace the data disk with an SSD? This really depends on you. You will see higher performance, but it might not be as noticeable as you think. It depends on how much you use the data storage and what kinds of files you read/write on a regular basis to know if it would be worth the additional cost. Boot time can be faster. Loading large datasets can be faster. Accessing lots of smaller files at once can be faster. Of course it is really hard to beat hard disks for their capacity and price, and they have gotten pretty fast over the years.

Data recovery is actually more expensive on an SSD. You are right, it is more difficult to recover data from an SSD than from a hard disk. They are much different beasts. We see electronic failures and often remove the NAND flash chips to read their data directly, then piece things back together. SSDs are generally more durable though. Something to beware of - some SSD models use always-on encryption, which means the data is encrypted by the controller whether or not the user enabled encryption or set a password. This means that if there is ever a problem with the SSD electronics and the controller is unusable, the data will be completely lost because there is no way to decrypt it since the encryption key(s) are stored only there.

However, you should have a backup first of all, and you should check it to make sure the backup is what you expect and works. You shouldn't need data recovery. It is indeed a last resort.

I see @Michael Kjörling also linked to the related story I was going to from The Tech Report on SSD endurance. "The SSD Endurance Experiment: They're all dead" The bottom line is that unless you have really really extreme workloads, and a very long upgrade cycle, the endurance of SSDs should not matter to you.

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That depends, unless you play games, only the OS and Programs really benefit from an SSD, which can fit on a 256 or 120 GB SSD. So no, a normal consumer does not need an SSD for media or other mass storage uses. Some creative applications use scratch disks, which can benefit from faster storage.

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