Linux Support for Hybrid Hard Drives?

christoofar asks: "HHDD (Hybrid Hard Disk Drive) technology has been receiving some buzz lately. The concept is not new, but Samsung has been working on a consumer version of HHDD that everyone can use. HHDDs are disk drives that carry onboard RAM (in this case, NAND flash) which is non-volatile and offers to speed boot times and writes to the disk. This carries enormous benefit to laptop users who need to keep their disk activity to a minimum in order to preserve battery life. Given that Microsoft is adding support for Hybrid Hard Drives in their upcoming Windows Vista release, what efforts are being undertaken in the Linux realm to use this new storage technology?"

Comments

Re:Is it me or does this seem pointless?

[msbsod]

Well, they only produce the isolinear chips for Star Fleet.
Seriously, the NAND flash memory stores the data immediately. It is a perfect write cache, because it does not forget the data. Almost perfect, because its write cycles are limited. But a more reliable file system would do the trick, too. Journaling is one way of making things more reliable. But, you have a good point. It is important that some data get written ASAP onto the medium. Unfortunately Linux file systems are not exactly the right choice if this is of importance for you. VMS would be a much better alternative. In order to utilize these hybrid disks it is also important to ensure that the important data gets written immediately, and that the hybrid disk knows which data needs to be cached in the flash memory. The disk allocation tables and directories are obviously important. But some databases might be important too. Bottom line is, the disks simply cannot be smart enough to handle all file systems and all applications. Therefore I agree with you, the whole thing is pointless. It would be much easier to back up some of the computers power lines with a battery, as part of the power supply, not as external UPS (stupid HV-LV-HV-LV conversion - HV=High voltage 110/230V, LV=3.3-12V). There are a few power supplies available which do exactly that (internal LV backup).

Re:It should just work

[AKAImBatman]

I'm guessing that it's not so much that it can't work that way, as it is that it would kill performance.

Today's operating systems try to do exactly what this drive is doing by pumping all reads and writes through the paging system. The problem is that the OS can't take a full performance boost from this or data will be lost in a crash or power loss. You may remember that EXT2FS could easily lose all the data you'd recently written if it wasn't unmounted properly. (It ticked me off when I tried to move RedHat 5.2 packages to a special partition, then found out that they had all disappeared on reboot because I hadn't explicitly unmounted the disk. *grumble*)

Since this technology has little to no chance of losing data in a power failure, the OS can be modified to write the blocks immediately. This could easily result in a performance increase of 2 to 3 times what you normally see today. The improvements in writing meta-data alone could easily provide this increase.

What to put in there?

[aspoon]

The question is not whether Linux will support the drive -- someone will eventually write one. The question is what files to put in there to make it boot faster. Perhaps should be done is to put the entire swap partition in there, and put those "hibernation" files in the swap. So it would resume fast, and would also make normal operations faster with the faster swap.

Why wait? Hack one up yourself!

[Myself]

You shouldn't have to wait for the drives to come out. Laptop drive controllers can address a master and a slave, they just don't have a slave drive connected in normal usage. I was just looking for an adapter to let me put a pair of CF cards in place of a 2.5" hard drive. (I can only find the single-card version in a 2.5" form factor, all the dual-card ones are for 3.5" mounting.) I figure, put a solid-state card in one slot and a microdrive in the other, and I've got a hybrid-drive laptop, right?

I just got rid of an old toughbook cf-25 that would've been perfect for this, as the drive mounting is gel and would easily accomodate an oddly shaped adapter instead of a regular drive. Or for the truly insane, a CF card piggybacked on a regular 2.5" drive! All I need is the ability to home-brew those little flex cables, and I'd be in business.

Write caching in flash...

[rew]

I'm not sure if write caching in the flash chips is a good idea...

Flash chips write at around 1Mb per second. Tops. Modern harddrives write around 50Mb per second. You'd need quite a lot of flash chips in parallel to top that.

Of course, you can cache acouple of writes on the laptop drive to prevent having to spin up the disk. But it is not going to be a speed issue.

Other good uses for this

[nial-in-a-box]

I think the real demand for flash-cache hard drives should be in the area of data loss prevention. Anyone who has any doubts about the fact that laptop hard drives are still way too fragile for the job needs to work at a help desk for a week. Any way to keep those drives spun down as much as possible should be seen as a good idea, since speed does not really matter much if you lose your data and/or need a new drive every three months simply because you like to move your laptop while it is running.

I know this just adds another point of failure to the mix with the addition of flash memory. However, with the apparent improvements in the quality of flash memory, I would expect one of these drives to outlast a current laptop drive by at least 50%. (Note: this is just idle speculation, but I don't know of any solid real-world statistics on laptop hard drive lifespan. I'm guessing laptop makers don't want us to know, either.)

I think that the point of drivers is, therefore, valid. There needs to be some sort of intelligence behind this system to allow frequently needed files to be held in cache in order for this to work effectively. Sure, you could build a drive that could try this on its own, but odds are you would totally throw out any performance or power advantage by doing so.

What I'd rather see anyway.

[IBitOBear]

I'd like to see linux have support for (and have hardware makers create) what SUN used to call NFS Accelerators. Basically add-on NV (or battery backed) memory sufficent to transparently cache write information. On my laptop I'd put it in my ExpressCard(tm) slot.

Then again I have been considering using an SD type card to contain the journal for my ext3 file system.

Actually, that combination; an ext3 file system in full data write-back journal mode, a solid-state flash device for that journal, and a "large" flush interval (more than the default five seconds) could accomplish essentially the same thing.

I wonder what the flash wear rate would be...? Do they make NAND SD cards?

(etc. od nausium. ahmen.)

Re:It should just work

[Nethemas the Great]

If access to drive contents are bound to runtime drivers then that content can be made bound to DRM. Am I the only one noticing a nice little trend happening...

--Neth