I'm considering getting an SSD drive to run as the primary OS partition. As I understand, this should provide a substantial improvement in performance.
The swap partition will be largely random seeks and so should benefit from the speed. On the other hand, it will be constantly written to which will wear out the drive faster.
From MSDN Blogs > Engineering Windows 7 > Support and Q&A for Solid-State Drives:
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.
In fact, given typical pagefile reference patterns and the favorable performance characteristics SSDs have on those patterns, there are few files better than the pagefile to place on an SSD.
Here is some S.M.A.R.T. data from an OCZ-AGILITY SSD that I have used in a Linux laptop for around two years.
I have a swap partition on the disk, and the only "tweak" I've made is to set swappiness = 0 in Linux. The windows swap profile is more or less like Linux swappiness = 0.
It's my personal laptop, so it's not used 8 hours a day (more like 1.5 hours), but I do quite a lot of development on it, so there is a lot of file creation going on.
9 Power_On_Hours 1199
12 Power_Cycle_Count 2753
184 Initial_Bad_Block_Coun 0
195 Program_Failure_Blk_Ct 0
196 Erase_Failure_Blk_Ct 0
197 Read_Failure_Blk_Ct 0
198 Read_Sectors_Tot_Ct 1311815826
199 Write_Sectors_Tot_Ct 1546123387
200 Read_Commands_Tot_Ct 22347850
201 Write_Commands_Tot_Ct 31599623
202 Error_Bits_Flash_Tot_Ct 55136
203 Corr_Read_Errors_Tot_Ct 54890
204 Bad_Block_Full_Flag 0
205 Max_PE_Count_Spec 10000
206 Min_Erase_Count 266
207 Max_Erase_Count 2166
208 Average_Erase_Count 842
209 Remaining_Lifetime_Perc 92
The interesting parts are:
So... I think it's safe to assume that the disk should last until I retire it for other reasons. (*touch wood) It's already too small...
Assuming the numbers scale, 40 hour/week would give a life time of at least 3-4 years - probably more, since I suspect I am more efficient at wearing out my disk at home... Fewer meetings... So, I think it's quite OK for a work machine, given the benefits.
100% / (40h/(1199/(2*52w)) * 8% = 3.6 // Did I get that right, eh...
So, my advice is: Get rid of the noisy mechanical drives and enjoy the silence :-)
It's awesome with an absolutely quiet laptop.
I retired the drive some time ago, after more than 5 years in service. I needed a bigger drive, and it was also nice to get a faster one. Some blocks have definitely died, but it looks like it could hold together a few more years.
By the way, it certainly survived the laptop it was originally installed in.
9 Power_On_Hours 3965
12 Power_Cycle_Count 8755
184 Initial_Bad_Block_Count 0
195 Program_Failure_Blk_Ct 0
196 Erase_Failure_Blk_Ct 0
197 Read_Failure_Blk_Ct 0
198 Read_Sectors_Tot_Ct 5438181603
199 Write_Sectors_Tot_Ct 4223860468
200 Read_Commands_Tot_Ct 108147770
201 Write_Commands_Tot_Ct 87443515
202 Error_Bits_Flash_Tot_Ct 364621
203 Corr_Read_Errors_Tot_Ct 350922
204 Bad_Block_Full_Flag 0
205 Max_PE_Count_Spec 10000
206 Min_Erase_Count 940
207 Max_Erase_Count 7808
208 Average_Erase_Count 3119
209 Remaining_Lifetime_Perc 69
211 SATA_Error_Ct_CRC 0
212 SATA_Error_Ct_Handshake 0
213 Indilinx_Internal 0
I have a better answer: Why, when you can just buy more RAM? RAM is as cheap or cheaper than SSD space. It's also much faster, and it will never (well, almost never) degrade like SSD drives do.
Swapping memory to disk is a symptom of not enough RAM. If you need to speed up swapping, don't speed up the swap disk, upgrade your RAM and the swapping will go away. Swapping should be considered a last-resort backup plan anyway.
A lot of people are saying "don't swap if you can help it", but this is misleading, at least for Windows (and probably for Linux too). Windows, esp. recent versions, will always try to fill up RAM with cached data that it thinks is going to be needed quickly, and will deliberately swap other stuff to disk. It does this irrespective of how much RAM you have. I have 4GB, only half in use, but swapping still happens. Disabling swapping is a bad idea too, because some programs can require huge amounts of memory reserved for them (think Photoshop), and you can easily get out of memory messages. It depends on usage, but swapping is always useful to have for extreme situations.
So SSDs are not a replacement for RAM (saying "get more RAM" is missing the point) but a possibly faster alternative to virtual memory on hard disks. Take a look at this review to see how SSDs can leave mechanical hard drives in the dust: "Hard-Drive Roundup June 2010"
Also remember it's the IOPS figure that's far more important than the transfer rate.
Another thing to consider is whether your current swap drive is also your main drive. For most people, the answer will be yes. That means the hard drive is having to access paged virtual memory whilst also accessing data and programs. In this case, having an SSD for paging is likely to make a noticeable improvement.
I'm looking for somebody who's tried this to give definitive info on performance, but on paper the case looks clear-cut.
If possible, you might want to use a secondary platter hard drive as the location for virtual memory. If you don't have one, it's still recommended to have a page file, but you might want to disable it for extra disk space. It's all up to you whether to decrease memory load or more disk space is important...
2016 Update
Performance
Some more fresh data about SSDs nowadays. They typically read, write 500 MB/s. A normal decent RAM's I/O is around 10-20 GB/s. However PCI-e SSD exist; they do have a good I/O rate (1-2 GB/s), but still they do perform like RAM in early-mid 2000s.
Performance ratios are:
If you did have an HDD, your virtual memory might get a good increase in performance.
Price
Regular SSD became cheap, but PCIe SSD with good I/O is not really cheap yet. Just do the math; out of PCI-e SSD price you can buy a new motherboard with new RAM, and voila, problem solved.
On the other hand, since SSD became more affordable, they are very much available for low money, and actually I will reuse my old 96 GB SSD as virtual memory. I can't really sell it, so I can use it for virtual memory. Well, why not? It is still better than an HDD. If you have to have a page file, put it on a legacy drive.
Reliability
The following test shows that many of them fail after a while.
100-600 terabytes are really a lot of I/O, and if you have let's say 48 GB virtual memory, if you read and write all in and out, it means at least 2000 iteration before the first bad sectors, but if you have a reliable disk, it is more like 10000 or more. I would assume it is more than two or three years of usage.
Sum
I would use it as a virtual drive if I really need it, but if it is an available option, just expand your RAM as far as you can in necessity. Use this virtual memory only if you run out of options. On the other hand, you can use your older SSD for this purpose, and you can replace it for 30-40 USD any time if fails (probably won't for a long while), it can be useful.
PCI-e SSD for virtual memory: if you want to burn money, or if you have absolutely no other choice.
One last sidenote: if you now have only HDD, go and get an SSD, migrate your operating system, you will feel like you bought a new computer.
Patrick Regan's answer about "swappiness" is pretty spot on: Depending on your usage, it might be fine, and if you're using Linux you can tweak "vm.swappiness" in sysctl (as described in an earlier question) for your use.
So I'm tempted to say yes, as long as you give lots of disk to your swap. I've been hearing lots about the internal controllers on SSD drives having super-tweaked algorithms to combat write wear, so in theory this would help -- give it lots of space, and set the kernel swappiness level low, and the SSD controller can spread the writes out and prevent any wear trouble.
So that got me to wondering what the largest swap partition could be. I locked onto your mention of "swap partition" and thought "Linux", so I looked into the maximums there.
It turns out you can create ridiculous things like 16 TB swap partitions, at least based on the kernel math. mkswap might not be able to actually initialize that partition, but the kernel supports it. However, the kernel can't use it. According to this, 16 GB is about the biggest swap partition you can make and use in a modern Linux kernel.
So yes, you can, if your usage is going to be fairly swap-free. If you'll be swap-heavy, though, maybe a cheapo USB key for ReadyBoost (or the Unix equivalent) would be a better fit -- that way when your swapping destroys the device from overwriting, it'll be cheap to replace and won't cost you the price of another SSD.
Although the random read of SSD drives is very good, the random write performance can be very bad. Apparently some SSDs only provide 12 write IOPS, which is only a tenth of what a standard rotational disk provides(~120 IOPS), and even faster SSDs like the Super Talent SSD may only provide 50 random write IOPS.
On the other hand, it is possible for an SSD to perform thousands of operations per second, for example the Intel X25-M 160 GB 34 nm MLC G2 can perform 86001 (according to the Intel specification sheet) or even 153342 random write IOPS of 4k blocks.
So in conclusion, the swap performance of your SSD may well be better, but do not assume that this will be the case until you have checked the number of random write IOPS your SSD can achieve.
[1]: http://download.intel.com/design/flash/nand/mainstream/322208.pdf
FWIW: I've been using my pagefile.sys on my Intel SSD, for 10 months continuously. I don't know about Windows Vista or newer, but on Windows XP turning OFF the pagefile seems like a really bad idea. Windows must thrash on something, so thrashing on an SSD is much better than thrashing on a traditional HD ;-)
If this actually decreases the lifespan of the SSD, so what? I'll be buying larger ones probably once / year as the prices continually drop. At this exact moment in time, you will spend about US$2 / GB.
I would be inclined to say that the performance gain from it is not worth it, especially if you have a lot of RAM. If you have at least 2GB RAM, you probably won't page a ton anyway so the benefits would be minimal. Not to mention that SSD sizes are relatively small, so you may not want to eat up a few GB worth of pagefile on it anyway.
I think it would depend on how much RAM you have and how your "swappiness" is set. I have a swap set up on my computers, but if I don't hibernate, I rarely write to it. I tend to not max out my RAM usage. But if you know you're hitting swap a lot, I'd say no. If you don't hit it a lot, I'd say go for it.
Unless you need the swap file (for suspend to disk for example), I would simply turn swapping off and get rid of your swap partition.
The point of swap is to provide an extra cache level. Since your SSD has a low latency, the gains of using swap are much lower.
If your system hardly ever swaps, then it makes even more sense to just get rid of it. I've been running a few Linux boxes without any swap for a few years now (on regular hard disk drives) without performance issues. Any box with more than 2 GB of RAM I just don't bother with swap for.
