5 ms·

Are Solid State Drives Worth the Money?

3 points by patrickk 16y ago

macemoneta 16y ago
It really depends on the platform and requirements. On a desktop, a three-drive RAID0 provides about the same performance, and gives you nearly 40x the storage for a given price-point. On a mobile platform the physical space, vibration/motion, and power constraints coupled with the increased performance may make SSDs worthwhile.
- moe 16y ago
  On a desktop, a three-drive RAID0 provides about the same performance, and gives you nearly 40x the storage for a given price-point. Quite a terrible idea unless you enjoy backup recovery sessions. If the noise of 3 drives doesn't bother you then you can just as well get 4 and setup a RAID10, which is nearly as fast but much less likely to fail.
  - macemoneta 16y ago
    I back up several times a day, automatically. I've run RAID arrays for years with no problems, but all drives eventually fail. An SSD is internally a RAID0 that can be up to 16 wide (that's how they get their performance). Used and managed properly (including proper backup and recovery), RAID0 works very well with good quality drives. If you have noise problems, then you likely have vibration issues that will shorten the life of your drives. I use anti-vibration mounts for all hard drives, and I hear my (quiet, anti-vibration mounted) fans more than I hear my drives. I also spin down the backup drives when they are not in use, so they add no additional noise.
    - moe 16y ago
      An SSD is internally a RAID0 that can be up to 16 wide (that's how they get their performance). Erm. Actually they get their performance because they write to NAND instead of spinning platters. SSD controllers are also quite a bit smarter than plain RAID0. RAID0 works very well with good quality drives. A RAID0 over three disks has about 1/3 the MTBF of a single disk. That can still be a worthwhile trade-off if you need the extra capacity, but if you're mostly after performance and reliability then a pair of SSDs, or even a single SSD, is the better choice.
      - macemoneta 16y ago
        You'll probably find this interesting reading on the internal architecture of SSDs: http://www.denali.com/wordpress/index.php/dmr/2010/02/02/ssd-interfaces-and-performance-effects Also, while RAID0 reduces the MTBF, it's not linear. Drive life is not magically shortened as a result of the drive being in a RAID array (if you take care to isolate synchronous vibration). The life of the array is equal to the shortest drive life. In other words, if a drive would have failed after 25,000 hours in standalone operation, it will still fail in 25,000 hours in an array. The other drives may run to 100,000 hours, but it's a "weakest link" failure mode.
        moe 16y ago
        Also, while RAID0 reduces the MTBF, it's not linear. Well, it is inverse proportional. The life of the array is equal to the shortest drive life. Erm. To be clear: Your risk of having a RAID0-set (over 3 disks) fail during a given timespan is 3 times higher than having a single-disk-"set" fail in the same timespan. In other words, if a drive would have failed after 25,000 hours in standalone operation, it will still fail in 25,000 hours in an array. That calculation makes no sense. If you have a single drive then that will fail, on average, after 25k hours. If you stripe over three of these drives then your array will, on average, fail after 8333 hours.
        macemoneta 16y ago
        While the probability of failure is nearly a function of the number of drives, the MTBF/MTTF calculations do not work that way. For example, if there were a probability of 5% that the disk would fail within three years, in a three disk RAID0 array, that probability of failure would be: P=(1-(1-.05)^3)=.14263 In other words, 14.3% probability of failure within three years. That doesn't mean it will fail in that time frame. It means if you have a large population of that configuration, that is the rate you would be dealing with for drive replacement planning. The MTBF and MTTF calculations apply to populations of drives (e.g. a given model) not to a given drive. The values provide no predictability for the failure of any specific drive. Using the values for that purpose is a common misapplication. A drive with a MTTF of 1,000,000 power-on hours can fail in 15 minutes or never during its useful life. As a result, a three drive array will have a higher probability of failure over a given interval, but the MTTF/MTBF of the drives is essentially unchanged. Think of it this way... The probability of winning the lottery is one in 20,000,000. The probability that someone (anyone) will win the lottery in a given week may be one out of ten - 10%. In other words, some person wins the lottery, on average, one time in ten weeks. That doesn't mean that your probability of winning the lottery is 10%. It also doesn't mean that the average probability of winning the lottery is 10%. It also doesn't change the probability of winning the lottery; it's still one in 20,000,000, even if three people win in a 10 week interval.
chrisbolt 16y ago
I'm spoiled by SSDs now. I've had an X25-M in my primary computer for almost a year now, and other computers feel so slow that I can't imagine going back. Even in servers, one X25-M can replace 4 15k RPM disks in RAID 10 for I/O load, not to mention the power savings.
ahoyhere 16y ago
I would never go back to regular HDDs. Quiet, cool, sipping battery life… go go gadget SSD!
AndrewDucker 16y ago
The Momentus XT seems to be a good compromise (4GB SSD that caches frequently used parts of a normal HD). I know a couple of friends with them, and they say that applications load vastly faster, and their machines also boot faster. It doesn't help with sustained throughput, but that's not normally a problem.
trustfundbaby 16y ago
Totally worth it with one major caveat. SSD drives don't actually delete stuff when you 'delete' them, it just tells your OS that that it can write to that space. Normal hard drives do this too, the problem comes when you actually go to write stuff to the space that is 'marked for deletion'. Unlike normal hard drives that just overwrite the disk space, SSD drives can only write to disk in groups called 'blocks'. So when the drive is filled up with stuff (or you've been using it for some time), it has to corral the block, make sure its safe to write to, if it isn't, it wipes it, before finally writing to it ... which is really slow. This manifests itself in your system basically freezing on you from time to time after you've been using it. Its fully explained here http://www.anandtech.com/show/2738/8 http://www.anandtech.com/show/2738/8 It can be REALLY frustrating, but even with that ... I would NEVER NEVER go back to a normal hard drive. Why? My photoshop opens in 7 seconds, Netbeans (bloated Java IDE) in 10, Windows XP boots in bootcamp in 2 minutes, and OS X is fully loaded in 30 seconds. So yeah ... you can pry my ssd from my cold, dead, mutilated fingers. There is a TRIM OS command that allows your OS to basically clean out the space on your hard drive that is marked for deletion while you're not using the computer, so that this problem does not occur, but OS X does not support it ... Windows 7 and Linux are the only OS's I know that do. http://www.anandtech.com/show/2738/10 http://www.anandtech.com/show/2738/10 The other thing to consider is that SSDs are very fast on sustained writes ... copying a 1GB file from one location to another. However, modern OS'es employ frequent but small writes in their operation ... and certain drives that look good on paper stink up the joint in this department (things have changed recently though, since anandtech called them out on it). What you want to do when you're looking at specs is find out what the throughput is (MB/s) for writes on 1KB, 4KB pieces of data, and compare it to the sustained write speeds, to see how big the difference is. If you want a shortcut ... buy an intel SSD ... and thank me later.

3 points by patrickk 16y ago

It really depends on the platform and requirements. On a desktop, a three-drive RAID0 provides about the same performance, and gives you nearly 40x the storage for a given price-point. On a mobile platform the physical space, vibration/motion, and power constraints coupled with the increased performance may make SSDs worthwhile.

moe 16y ago
On a desktop, a three-drive RAID0 provides about the same performance, and gives you nearly 40x the storage for a given price-point. Quite a terrible idea unless you enjoy backup recovery sessions. If the noise of 3 drives doesn't bother you then you can just as well get 4 and setup a RAID10, which is nearly as fast but much less likely to fail.
- macemoneta 16y ago
  I back up several times a day, automatically. I've run RAID arrays for years with no problems, but all drives eventually fail. An SSD is internally a RAID0 that can be up to 16 wide (that's how they get their performance). Used and managed properly (including proper backup and recovery), RAID0 works very well with good quality drives. If you have noise problems, then you likely have vibration issues that will shorten the life of your drives. I use anti-vibration mounts for all hard drives, and I hear my (quiet, anti-vibration mounted) fans more than I hear my drives. I also spin down the backup drives when they are not in use, so they add no additional noise.
  - moe 16y ago
    An SSD is internally a RAID0 that can be up to 16 wide (that's how they get their performance). Erm. Actually they get their performance because they write to NAND instead of spinning platters. SSD controllers are also quite a bit smarter than plain RAID0. RAID0 works very well with good quality drives. A RAID0 over three disks has about 1/3 the MTBF of a single disk. That can still be a worthwhile trade-off if you need the extra capacity, but if you're mostly after performance and reliability then a pair of SSDs, or even a single SSD, is the better choice.
    - macemoneta 16y ago
      You'll probably find this interesting reading on the internal architecture of SSDs: http://www.denali.com/wordpress/index.php/dmr/2010/02/02/ssd-interfaces-and-performance-effects Also, while RAID0 reduces the MTBF, it's not linear. Drive life is not magically shortened as a result of the drive being in a RAID array (if you take care to isolate synchronous vibration). The life of the array is equal to the shortest drive life. In other words, if a drive would have failed after 25,000 hours in standalone operation, it will still fail in 25,000 hours in an array. The other drives may run to 100,000 hours, but it's a "weakest link" failure mode.
      - moe 16y ago
        Also, while RAID0 reduces the MTBF, it's not linear. Well, it is inverse proportional. The life of the array is equal to the shortest drive life. Erm. To be clear: Your risk of having a RAID0-set (over 3 disks) fail during a given timespan is 3 times higher than having a single-disk-"set" fail in the same timespan. In other words, if a drive would have failed after 25,000 hours in standalone operation, it will still fail in 25,000 hours in an array. That calculation makes no sense. If you have a single drive then that will fail, on average, after 25k hours. If you stripe over three of these drives then your array will, on average, fail after 8333 hours.
        macemoneta 16y ago
        While the probability of failure is nearly a function of the number of drives, the MTBF/MTTF calculations do not work that way. For example, if there were a probability of 5% that the disk would fail within three years, in a three disk RAID0 array, that probability of failure would be: P=(1-(1-.05)^3)=.14263 In other words, 14.3% probability of failure within three years. That doesn't mean it will fail in that time frame. It means if you have a large population of that configuration, that is the rate you would be dealing with for drive replacement planning. The MTBF and MTTF calculations apply to populations of drives (e.g. a given model) not to a given drive. The values provide no predictability for the failure of any specific drive. Using the values for that purpose is a common misapplication. A drive with a MTTF of 1,000,000 power-on hours can fail in 15 minutes or never during its useful life. As a result, a three drive array will have a higher probability of failure over a given interval, but the MTTF/MTBF of the drives is essentially unchanged. Think of it this way... The probability of winning the lottery is one in 20,000,000. The probability that someone (anyone) will win the lottery in a given week may be one out of ten - 10%. In other words, some person wins the lottery, on average, one time in ten weeks. That doesn't mean that your probability of winning the lottery is 10%. It also doesn't mean that the average probability of winning the lottery is 10%. It also doesn't change the probability of winning the lottery; it's still one in 20,000,000, even if three people win in a 10 week interval.

chrisbolt 16y ago

I'm spoiled by SSDs now. I've had an X25-M in my primary computer for almost a year now, and other computers feel so slow that I can't imagine going back. Even in servers, one X25-M can replace 4 15k RPM disks in RAID 10 for I/O load, not to mention the power savings.

ahoyhere 16y ago

I would never go back to regular HDDs. Quiet, cool, sipping battery life… go go gadget SSD!

AndrewDucker 16y ago

The Momentus XT seems to be a good compromise (4GB SSD that caches frequently used parts of a normal HD). I know a couple of friends with them, and they say that applications load vastly faster, and their machines also boot faster. It doesn't help with sustained throughput, but that's not normally a problem.

trustfundbaby 16y ago

Totally worth it with one major caveat. SSD drives don't actually delete stuff when you 'delete' them, it just tells your OS that that it can write to that space. Normal hard drives do this too, the problem comes when you actually go to write stuff to the space that is 'marked for deletion'. Unlike normal hard drives that just overwrite the disk space, SSD drives can only write to disk in groups called 'blocks'. So when the drive is filled up with stuff (or you've been using it for some time), it has to corral the block, make sure its safe to write to, if it isn't, it wipes it, before finally writing to it ... which is really slow. This manifests itself in your system basically freezing on you from time to time after you've been using it. Its fully explained here http://www.anandtech.com/show/2738/8 http://www.anandtech.com/show/2738/8 It can be REALLY frustrating, but even with that ... I would NEVER NEVER go back to a normal hard drive. Why? My photoshop opens in 7 seconds, Netbeans (bloated Java IDE) in 10, Windows XP boots in bootcamp in 2 minutes, and OS X is fully loaded in 30 seconds. So yeah ... you can pry my ssd from my cold, dead, mutilated fingers. There is a TRIM OS command that allows your OS to basically clean out the space on your hard drive that is marked for deletion while you're not using the computer, so that this problem does not occur, but OS X does not support it ... Windows 7 and Linux are the only OS's I know that do. http://www.anandtech.com/show/2738/10 http://www.anandtech.com/show/2738/10 The other thing to consider is that SSDs are very fast on sustained writes ... copying a 1GB file from one location to another. However, modern OS'es employ frequent but small writes in their operation ... and certain drives that look good on paper stink up the joint in this department (things have changed recently though, since anandtech called them out on it). What you want to do when you're looking at specs is find out what the throughput is (MB/s) for writes on 1KB, 4KB pieces of data, and compare it to the sustained write speeds, to see how big the difference is. If you want a shortcut ... buy an intel SSD ... and thank me later.