Tuesday, November 20, 2012

Experience With Hybrid Solid State Hard Drives?

The 100 GB drive on my laptop is getting crowded.  (Time to wax unnostalgic for when a 5 MB hard drive for a PC cost $2000.)  I have already moved as much stuff off this drive to external disks as I can, but the problem is that when your hard drive gets below 20% free, virtual memory starts getting problematic, as it becomes harder and harder to find a contiguous block of disk space.  Yes, you can solve this problem -- temporarily -- by defragging your hard disk.  But when disk space is tight, this solution does not last long.  (I think at one time Windows would actually block this part of the disk from being allocated, but apparently not under XP.)

My thought is to get a hard disk that will take me years (or one feature length film's development) to fill.  I was looking at 500 GB and 750 GB hard drives for my notebook -- and these are dirt cheap.  But then I noticed this hybrid SSD/hard disk drive.  It looks like a hard drive with an extraordinarily large cache,  optimized to learn which tracks will be used repeatedly, instead of the traditional caching approach.  Supposedly boot time is much enhanced, and according to comments that I have read elsewhere, over a period of several days, it learns which tracks to keep in solid state memory.  I would assume that the tracks allocated to virtual memory would just scream compared to a traditional disk drive.

Any experience with these?  Is there any hazard to defragging one of these drives?

UPDATE: I confess, the temptation to go to a real SSD drive is strong.  Here's a 256 GB SSD drive for $217 that should be a real screamer on both read and write.  Of course, if I go to the 750 GB drive, I can allocate a bunch of disk space to a dedicated virtual memory block (yes, according to the comments, XP does support that).  But a 256 GB drive would be 150% gain on what I have now.  I rather doubt that this will be a problem in the time that I am likely to keep this notebook.

And here's a 500 GB Hybrid SSD (4 GB cache) for $49.95!  That's still 500% more space than I have now, at what a price!  I don't know what speed my current drive is, but I would not be surprised if it is only 5400 rpm; this is 7200 rpm.  Hmmm.  I wonder what it will be on Black Friday?

UPDATE 2: I called Staples, because they quoted $39.95 to install a drive, but that is apparently not for laptops, and does not include data transfer.  That turns out to be $49.95 for the install and $69.95 to transfer it over.  Suddenly, it is getting more attractive to do this myself.

15 comments:

TriggerFinger said...

I have a desktop running a similar setup in software, with two separate drives (1TB HD and 128GB SSD). It's not noticeably faster than a bare HD. It would probably benchmark maybe 10%-15% faster in normal usage, but it won't be a huge improvement.

That's with a "cache" 10% the size of total storage. Based on the price of the drive you linked, you're getting less space than that. 8GB, according to one of the comments. I'd expect performance gain to be less than I see, allowing for variances in implementation.

Not trying to say it's a bad purchase or won't be somewhat faster. I am trying to say you shouldn't expect a big speed boost.

TriggerFinger said...

... OTOH, I don't think the desktop system I was talking about has ever gone into swap, so we may have significantly different use cases there.

Josh said...

This CodingHorror piece is somewhat out-of-date, but still gives relevant information -- especially the warning about TRIM support for full SSDs, and that both SSDs and hybrid disks have had a number of lackluster offerings.

I've used one (the second generation Momentus), and they are faster than platter disks, often by significant amounts. The flash memory is only usually a single chip, so it doesn't go as fast as the heavily parallel chips on an SSD can, but it's still much quicker at read access than anything with moving parts can be. Generally no improvement on write speed, though. The difference won't be in general performance, though; it only affects things like boot speed and programs as they first open. That can be a big deal for some: it changes first start times to browser or editor by up to an order of magnitude, and my lead programmer at work insists on them. If you're not so focused on that, and don't mind short load times during read from disk moments, it won't be a big deal.

No obvious issue with defragments -- you get a slight drop in performance if the cached data isn't where the disk controller expects, but your defrag shouldn't cause that normally anyway -- and unlike SSDs you don't really need the TRIM command.

The trick is that the gap between platter disks and SSDs is increasingly small as NAND prices drop and as laptops remain less useful devices for gaming and for large development work. If you're working on the components for a feature-length film in raw format, you don't want them on a 2.5" disk of any type: you want them on a mirrored RAID (probably with an external backup) on a desktop system that can churn them overnight and has a real processor.

((In Windows XP, you can also set a static minimum page file size to prevent new files from writing over the area a page file is likely to be assigned. It'll at least save you some defrags, although there's a deeper problem at >80% capacity as the disk controller has to use the less efficient internal edge of the disk.))

Moose said...

I'd say you'd not see a speed up of an older system. I'd just to with a fast mechanical HD (not a hybrid). You're limiting factor will be your storage adapter.

Clayton said...

Very useful. Yes, I wasn't expecting dramatic improvements on writes. The only way to make cache improvement performance on writes is if the cache only updates to the hard disk on file close or worse, system shutdown. Both are great performance gains, at the cost of reliability. (On a multiuser system, there are other problems, but there are not many non-server PCs with this issue, I would guess.)

Moose said...

So I'd say the biggest surprise to people unused to SSDs is that they have a finite life, and behave differently from mechanical HD's - you shouldn't defrag them, they "wear out" in a short time compared to mechanical HD's, etc. What is your laptop model, Clayton? What's the speed of your storage adapter?

Clayton said...

That was my understanding -- that SSDs, because they are built using EEROM technology (or whatever the modern equivalent is) only have a limited lifespan. That's why I asked about defrag. Of course, how long do hard disks last? The current drive is about five years old, and giving no signs of giving up.

It is an HP DV5126. My guess is that the storage adapter could be the limiting factor. I confess, when it isn't grinding away on virtual memory operations (which I am sure are shortening the drive's life), my PC is astonishingly quick, in spite of being at least a five year old PC. The other PC is a Compaq that was issued to me by HP in 2003, and perhaps because it has lots of free disk space, it runs pretty darn fast (although not quite as fast as the DV5126).

Jim said...

I think the better (maybe all by now) SSDs write in random sectors so that they have a longer life. You might want to check on that.

Moose said...

is that an ATA or SATA storage adapter? I can't find it on the HP website..

PhaseMargin said...

Personally, I like these drives. I've got one and they work great.

But the more I've talked to the guys who design the SSD controllers, the less I like flash-based SSD drives. You think things are bad with HDDs when they fill up to 80%? At least with an HDD you can't wear out the drive by writing to it. Flash drives get a phenomenon called Write Amplification whenever the drive gets above about 33% full where a single write actually causes more data to be written to the drive. Basically, the page size of the data you have to write to the flash chip is much larger than the "sector" on the SSD so the wear-leveling algorithms in the SSD controller have to copy whole blocks of data to new pages to write your little chunk of data. Defragging an SSD is frankly a bad idea as you can begin to see why (not that you should need it -- it's the latency of seeking and spinning that you minimize for an HDD and that latency is far, far longer than accessing a new page in an SSD).

All in all, write amplification is a real drive killer and most SSDs have a relatively short lifetime if you even hit 50% capacity. The Sandforce controllers are by far the best at minimizing Write Amplification, but after talking to SSD controller designers I'm not sure I'd be willing to trust my data to an SSD. Those guys are doing some pretty wild signal processing on what in theory should be digital bits stored in the flash drive to try and keep the things running longer.

Clayton said...

The DV5126 uses a SATA/150 controller. I see Staples is offering to install and copy drives for $39.95 -- that is worth paying their slightly higher prices for a drive. And maybe I will just settle for a 500 GB 7200 rpm drive.

Mauser said...

I've also learned that "Defrag" and "Optimize" are two different things. The windows Defragger, and other programs don't make your files each into one continuous chunk.

Sigivald said...

1) Always have a backup. When you do, it doesn't matter if your SSD dies, or your rotary disk.

2) If you need a lot of virtual memory on disk, you're doing something wrong - if it's not being used, it's useless, and if it IS being read from, ever, you're absolutely destroying performance.

RAM is cheap, performance matters. Never page to disk if you can help it. The only good virtual memory is unused virtual memory (or a place to cope with memory leaks, by paging never-again-to-be-accessed-but-never-deallocated waste).

3) Get a real SSD if you care about performance more than immense space.

4) If you really need both, I suggest a laptop with room for two drives, and one of each.

Clayton said...

Unfortunately, my PC is already as fully stocked with RAM as it will tolerate. There is some question as to whether this particular PC can go above 240 GB on a hard disk because of CMOS limitations. I am going to find that out this evening. I may be able to save some money because I can't go larger than 240 GB.

I am not too keen on spending money on a newer and faster laptop at the moment. The snowplow is already going to be a bit spendy.

Rick C said...

If you've never done it, swapping hard drives on a laptop is usually pretty darn easy: unscrew 1-3 screws holding the drive to the frame of the laptop, and unplug it. Laptop drives don't even usually use a cable--they plug right in to a socket.