Linked by Thom Holwerda on Thu 27th Sep 2012 19:36 UTC
Apple I bought a brand new iMac on Tuesday. I'm pretty sure this will come as a surprise to some, so I figured I might as well offer some background information about this choice - maybe it'll help other people who are also pondering what to buy as their next computer.
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UltraZelda64
Member since:
2006-12-05

I agree, this is the way to go if you happen to have an SSD. SSD for the system, hard drive for data. But I have to admit that I don't trust SSDs for the long term--even when used as a system drive. For example, if you regularly do a fresh install of your OS while keeping your /home directory intact, and you use a distro that has a release cycle of under a year, how many OS installs will you be able to do before bits start to go bad? Never mind the typical package updates throughout the lifespan of a distro; there are usually lots of those.

The fact that these things have to even be considered makes hard drives a more attractive choice in my opinion. Also, if you're a distro hopper you may run into problems sooner. What about swap space... should you put your swap partition on a hard drive, and then suffer the slowdown of using a hard drive anyway (eliminating one of SSD's biggest advantages) as soon you start running out of RAM--all because the SSD cannot be trusted for frequent rewrites?

Instead of getting one expensive drive that is just big enough to hold one OS and does not have proven reliability, I honestly think you'd be better off just getting a larger hard drive and partitioning it. Or even get a smaller "system" hard drive, and a bigger one for data. Sure, hard drives are also not known for their low failure rate, but at least they've been tried, tested and proven over the decades. It's a technology you can at least somewhat trust.

Modern computers and hard drives are so damn fast anyway, I honestly can't imagine an SSD being that big of an improvement over a good quality hard drive, performance-wise. Where SSD can truly beat the shit out of hard drives, though, is in laptops and similar portable devices; no moving parts means no physical damage, crashing, and data loss by accidentally dropping or bumping the computer. IMO, that is where SSDs truly shine. Then again, even in laptops I often hear about the battery or a corrupt/infected Windows installs far more often than a crashed hard drive.

Reply Parent Score: 2

Morgan Member since:
2005-06-29

I pretty much agree with you all the way, which is why I have yet to dive into the SSD world.

You mentioned swap and "running out of RAM" but most machines these days have 4GB or more of RAM out of the box, even laptops. While I don't think one should run without swap, I really don't see the benefit of putting it on an SSD if it will rarely be touched. The exception would be older machines limited to 2GB of RAM or less, though the cost/benefit equation of an SSD in such a machine is something else to ponder.

Reply Parent Score: 2

gfx1 Member since:
2006-01-20

OSX runs happily out of RAM with 4GB and Firefox running. After replacing it with 8GB I haven't heard complaints...

Reply Parent Score: 1

UltraZelda64 Member since:
2006-12-05

Really the main benefit would be to have something to fall back on in case a runaway process starts leaking memory. Other than that... well, swap is mostly pointless at this point when you've got 4-plus gigs of RAM. Even if I had a whopping 16GB of RAM, I would probably still set up, say, 256MB swap, just in case.

I was mostly referring to slightly older machines that may only have 1-2GB RAM. The POS Dell I'm on (from 2006), for example, has a dual-core AMD64 processor with only a gig of memory, and it can only handle a max of two gigs. In fact, I recently downgraded from a 64-bit OS to 32-bit to gain performance improvements by not swapping so much. And so far, it's helped.

Still though, if it's a desktop machine in question, if you go the route you mentioned by using SSD for system and HDD for data, it'd be simple and practical to set up a small swap partition on the HDD. And as you mentioned the newest machines come with enough memory that they will probably never need to swap anyway, but you could still have it just for a little extra protection.

Reply Parent Score: 2

WereCatf Member since:
2006-02-15

But I have to admit that I don't trust SSDs for the long term--even when used as a system drive.


A regular consumer-oriented SSD should last around 10 years as a system drive just fine, even with swap on it. There are several websites about this, including specific burn-in benchmarks that just keep reading/writing the SSD until it goes bust.

Modern computers and hard drives are so damn fast anyway, I honestly can't imagine an SSD being that big of an improvement over a good quality hard drive


The difference is like a night and day. SSDs especially excel at reading small files and/or fragments that are scattered all over the disk because of the miniscule seek times. Out of curiosity I tested my regular HDDs the other day and got 7ms and 9ms seek times whereas a USB 3.0 stick got 0.05ms seek times. That's 140 times faster. And guess what? Typical OS-files and program libraries and binaries tend to be small files, scattered all over the place.

Regular HDDs are still good for sequential data, but even there SSDs these days trump HDDs in speeds, with some going up to 500MB/s sustained sequential write speeds.

Reply Parent Score: 3

UltraZelda64 Member since:
2006-12-05

Well, two things. First, I'm not sure I can believe that "10 years" figure; I've done some reading about SSDs, and it doesn't seem totally believable to me. Not for a system drive with swap and all your data, at least. It just sounds too far-fetched. Maybe in a perfect world and in perfect conditions, but not in this world.

And second, SSDs definitely have the theoretical edge over hard drives when it comes to the speed of reading files that are laid out non-contiguously on the drive. But... at the same time, in all my time running Linux (exclusively for about 6 years), I have not had any major slowdowns due to fragmentation. It just doesn't happen. I was leery about moving entirely to an OS that doesn't even offer a native defragmentation program, but it turns out that it really is needed much less.

On the other hand, before I switched I was using Windows XP, and it seemed like I was running PerfectDisk every week or two just to keep the drive running at peak speed (especially the system drive). So... I guess the moral of the story here is that Windows users have more to gain in terms of performance than Linux users by using an SSD?

I recently found out about the free version of PerfectDisk and had my cousin install it on his Windows 7-based machine... as I expected, just one offline/boot defrag and one online defrag made a very noticeable performance improvement. So apparently on Windows a good defragging is still needed. [Note: Previously, I told him to install the free program Defraggler, which he used until then. IMO, PerfectDisk is a must... if I ran Windows today, I would no doubt buy another license for a recent version of the program.]

Reply Parent Score: 1

christian Member since:
2005-07-06

I agree, this is the way to go if you happen to have an SSD. SSD for the system, hard drive for data. But I have to admit that I don't trust SSDs for the long term--even when used as a system drive. For example, if you regularly do a fresh install of your OS while keeping your /home directory intact, and you use a distro that has a release cycle of under a year, how many OS installs will you be able to do before bits start to go bad? Never mind the typical package updates throughout the lifespan of a distro; there are usually lots of those.

The fact that these things have to even be considered makes hard drives a more attractive choice in my opinion. Also, if you're a distro hopper you may run into problems sooner. What about swap space... should you put your swap partition on a hard drive, and then suffer the slowdown of using a hard drive anyway (eliminating one of SSD's biggest advantages) as soon you start running out of RAM--all because the SSD cannot be trusted for frequent rewrites?



Do the maths. 3000 p/e cycles per block. So for a 128GB drive with ideal wear levelling, you can write ~3000 * 128GB. If you write 64GB a day (unlikely) you'd get 6000 days worth of writes. That's > 16 years.

My guess is your SSD will outlive your machine, and may well die a http://en.wikipedia.org/wiki/Whisker_(metallurgy) related death before the FLASH dies.

Reply Parent Score: 2

UltraZelda64 Member since:
2006-12-05

Do the maths. 3000 p/e cycles per block. So for a 128GB drive with ideal wear levelling, you can write ~3000 * 128GB. If you write 64GB a day (unlikely) you'd get 6000 days worth of writes. That's > 16 years.

I believe they "did the math" as well as controlled-climate testing when they came up with the conclusion that the Compact Disc would last up to 100 years, did they not? Also, I've had a few hard drives outlive the computer itself, so that's not saying a whole lot about the SSD. Especially when it's all theoretical anyway.

And in the previously mentioned case of swap use on an SSD, that same math will work out of your favor, speeding up the loss of bits on that device. Unless these drives actually swap bits from different partitions across the entire device. Do they?

Once these things have been in decent use in the real world for about 15-20 years and there is real-world evidence to back it up, I'll believe. ;) Of course, by then the newest SSDs of the time will undoubtedly be far more reliable than what there are now.

Reply Parent Score: 2

Alfman Member since:
2011-01-28

christian,

"Do the maths. 3000 p/e cycles per block. So for a 128GB drive with ideal wear levelling, you can write ~3000 * 128GB. If you write 64GB a day (unlikely) you'd get 6000 days worth of writes. That's > 16 years."


I've got a few issues with your calculation. Obviously "ideal wear levelling" doesn't exist generically: what's ideal for one pattern is non-ideal for other patterns. And in fact a 128GB SSD is likely to be comprised of at least 8 NAND chips, which for performance reasons are running in parallel and may not take part in distributed wear leveling. So removing your assumptions might decrease your calculation by at least a factor of 8.

We are also talking about reliability on it's own, but in real devices reliability is one of many conflicting goals: performance, capacity, cost, dimensions. etc. The point I'm trying to make is that it's not safe to make assumptions. Even if the MTBF was 100% accurate, it only describes a curve with a multitude of failure points. Even with 3-5 years MTBF, you can still fail in a few months time. I'm just recommending those with write-heavy data loads take extra precaution against data loss with flash drives.

There was a study someone did correlating the jitter in flash performance to it's remaining data longevity. The older flash cells are, the more time it takes to re-program them. I'll try to find a link to it. It could offer a way of getting feedback about how much life is remaining on one's SSD.

Reply Parent Score: 2

ggeldenhuys Member since:
2006-11-13

Modern computers and hard drives are so damn fast anyway, I honestly can't imagine an SSD being that big of an improvement over a good quality hard drive, performance-wise.

I've only moved to a SSD drive some 3 months ago. There is a HUGE difference in performance. Applications (no matter how big) load near instant. Any apps that use disk IO are dramatically improved.

Don't believe me, view the many Macbook Pro SSD vs Standard HDD videos. It is really just as you see it in those videos. The nice thing of those Macbook Pro comparisons is that you know the hardware is identical, just the hard drives are different.

I have a 128GB OCZ Vertex 4 SSD. With 460MB/s read and write performance and a constant 0.02ms access time, standard hard drives simply pale in comparison. Obviously I still use large standard hard drives for general data storage, simply because they are cheap.

Reply Parent Score: 2