Hybrid drive

A hybrid drive or Hybrid Hard Drive (HHD) is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it uses a smaller solid-state drive (SSD) as a cache. The cache typically uses non-volatile flash memory, but some drives use battery backed RAM (a Hybrid RAM disk). The flash memory buffer can speed up repeated reads; a RAM buffer speeds both reads and writes, but must be written to backup storage when power is lost.

Samsung claims that a flash based hybrid offers numerous benefits, chief among them speed of data access and consequent faster computer boot process, [cite news|url=http://www.electronicsweekly.com/Articles/2006/07/26/39320/Samsung+says+flash+drive+boosts+speed+of+Windows+Vista.htm|title=Samsung says flash drive boosts speed of Windows Vista|publisher=Electronics Weekly|date=26 July, 2006|accessdate=2006-01-21] decreased power consumption, and improved reliability.

Samsung released the first hybrid drives, primarily for notebook computers, to OEMs in March 2007. [cite news|url=http://www.engadget.com/2007/03/07/samsungs-hybrid-hard-drive-hhd-released-to-oems/|first=Thomas|last=Ricker|publisher=Engadget|title=Samsung's Hybrid Hard Drive (HHD) released to OEMs|date=2007-03-07|accessdate=2007-04-25]

As of early 2008 the special features of hybrid drives are only taken advantage of by Microsoft's Windows Vista: the operating system files required for booting are stored in the fast flash memory, reducing boot time by about 20%.Fact|date=March 2008 Microsoft uses the name ReadyDrive to describe the software side of this technology. [ [http://www.skymonkey.org/index.php?s=hhds skymonkey.org] ] While hybrid drives are not required for Vista Premium certification of laptops, some confusion arose as to whether such drives would be mandatory. [cite news
url=http://arstechnica.com/journals/microsoft.ars/2006/6/14/4328
title=Hybrid hard drives are not a Vista Premium requirement
date=2006-06-14
accessdate=2008-02-16
last=Fischer
first=Ken
work=One Microsoft Way
publisher=Ars Technica]

The hybrid drive command interface will be standardized in the new revision 8 of the ATA standard.

A hybrid drive may be created from separate devices, managed by software, such as ReadyBoost.

Operation

Unlike most standard hard drives, the hybrid drive in its normal state has its platters at rest, with the motor not consuming power or generating heat. Any data written to the hybrid drive is written to the buffer; there is no risk of data loss in the event of power failure as the buffer's flash memory is not volatile. When reading data from the platters extra data is read and stored in buffer memory (which need not be non-volatile flash memory) in the hope of anticipating future requirements as in any disk cache. Data required for the next boot-up can be stored in the non-volatile buffer before closing down the computer.

The hybrid drive's platters will spin up to move data from the write buffer to the platters when nearly full, and to read data which is not in the cache.Fact|date=February 2007

Early estimates place the actual hard drive usage (when the platters are spinning) at anywhere between 1.25% [http://news.zdnet.co.uk/hardware/storage/0,39020366,39196323,00.htm Kanellos, Michael "Hybrid drive to extend notebook battery life" CNET News.com 26.04.2005] ] and 10%"Notebook Storage Gets Buffer" Maximum PC July 2005, pg. 15] for typical single users, although there are obviously situations where platter usage will be much higher, such as the encoding or editing of very large video files, producing reports from a database, etc.

Claimed benefits

Manufacturers claim several benefits of the hybrid drive over standard hard drives, especially for use in notebook computers.

;Decreased power consumption and heat generation:Because the platters will not have to be spinning as much, power consumed by the hard drive and dissipated as heat will be less than non-hybrid drives. For mobile computers the battery will power the computer for longer before needing recharging.

;Faster boot time, startup from hibernation:Using data in the flash cache, which has good performance for reading data, computers can quickly resume from hibernation.

;Decreased noise:The drives are silent when the motor is not running, and the fan can run slower or less frequently.

;Improved reliability:Head crashes due to impact to the computer while the platters are running are less likely.

;Improved performance:Writing to and reading from solid-state memory is faster than a hard drive (with the exception of small writes; see below). While the conventional volatile RAM cache of a normal disk drive is faster than flash memory, data is written to the platters relatively quickly and frequently to minimise the risk of data loss if power is lost.

Claimed Drawbacks

There are some inherent drawbacks to the use of hybrid drives: [http://www.skymonkey.org/index.php?s=hhds skymonkey: what are hybrid hard drives (HHDs)?] ] [http://blogs.zdnet.com/storage/?p=179 Hybrid drives: not so fast!] ] [A. Birrell, M. Isard, C. Thacker, T. Wobber. [http://research.microsoft.com/research/pubs/view.aspx?type=Technical%20Report&id=1032 A Design for High-Performance Flash Disks] In Operating Systems Review, 41(2), April 2007, pages 88-93.]

;Lower performance (access time) for non-cached data:If the data being accessed is not in the cache and the drive has spun down, access time will be greatly increased since the platters will need to spin-up.

;Lower performance for small disk writes:Flash memory is significantly slower for writing small data, an effect that is amplified by use of journaling file systems.

;Increased cost:Hybrid hard drives are currently more expensive than their non-hybrid counterparts, because of the higher cost of flash memory.

;Reduced lifetime:A hard drive, once spinning, suffers almost no wear. A significant proportion of wear arises during the spin-up and spin-down processes. Indeed, the number of spin-ups is often given as the indication of the lifetime of a hard drive.:Flash memory allows far fewer write cycles than a hard disk

;Increased perceived noise production:A hybrid hard drive, spinning up and down, may make drive noise more noticeable, especially with varying usage conditions (i.e., fans and hard drive spinning up on usage).

;Increased power usage with spin-ups:A hybrid drive requires spin-up and spin-down more often than a normal hard drive, which is often spinning constantly. Hard drives also draw more power during spin-up. [ [http://www.storagereview.com/guide2000/ref/hdd/op/spinPower.html StorageReview: Continuous Power vs. Peak Power at Spin-Up] ]

;Lower recoverability:Hybrid hard drives, based on storage to both a flash component and a hard drive component, and bound to use by a specific OS (i.e., Windows Vista), cannot be recovered after failure using classic hard drive recovery services.

Software Implementation

Windows Vista natively supports the use of hybrid drives (ReadyDrive).

The basic functionality described here may also be implemented purely in software, using system memory instead of a buffer on the hard drive. Often, performance of the buffer can be more effective, since the speed is now limited by the system memory bandwidth, not the hard drive interface bandwidth. Examples of such a system include the SuperCache-II software system, and Windows Vista ReadyBoost.

Hybrid RAM Disk

The Hybrid RAM Disk uses a large buffer of volatile SDRAM memory with battery backup instead of flash memory to cache hard disk data during normal use. The buffer reduces time and energy spent accessing the hard disk. Because the RAM cache needs to be filled at startup, hybrid RAM disks may not speed the start-up process as much as flash based hybrid disks.

Frequently accessed data is stored in DRAM, while all the data is stored in hard disk. As a result, the hard disk only needs to be accessed when the processor requests data that is not frequently used.

Hybrid RAM Disks are claimed to offer significantly faster read-write speeds compared to standard hard disks.

Some RAM based SSDs may be used in combination with a hard disk to create a hybrid RAM disk.

Platinum hard disk drive

A Platinum hard disk drive is a hybrid RAM disk using 1 GB SDRAM as cache and 2.5 inch drive as target drive. Platinum HDD is managed by memory layer control devise called DTS chip inside the drive. The cache algorithm is 100% write back policy. To achieve this, the drive uses a capacitor to store power inside the drive. [http://www.nordichardware.com/news,6747.html Platinum HDD - combining the harddrive with a DRAM | NordicHardware ] ] The IO performance comes from SDRAM with is connecting 64bit internal BUS shows 10 to 100 time IO performance than traditional HDD.

The DTS intelligent function loads the most frequency Block IO and maintains them. One of example is quick boot manner. Whenever a system boots up using this hard drive, the Platinum drive pre-reads OS boot up sectors and application programs when it was called at last boot. Therefore Platinum drive effects boot up time enhancing any version, any type of Operating System such as Windows XP, Windows2003, Linux and UNIX. Platinum HDD are claimed to offer significantly faster read-write speeds from 10 to 100 times depends on the data size and power savings, compared to standard hard disks. It shows great performance under multiple users environment. For instance, virtual OS environment as VMware and XEN, Hybrid RAM disk performs big different performance result. I/O intensive application, data frequently application are good fits usage.The market position of Platinum HDD drive is SDRAM performance at 15Krpm HDD cost. Platinum HDD also mentioned that low electric power than traditional 3.5inch HDD (11watt VS 25watt).

See also

* Disk drive
* Solid-state drive
* Intel Turbo Memory
* ReadyDrive
* Non-volatile memory

References

External links

* [http://www.hybridstorage.org/index.html Hybrid Storage Alliance]
* [http://www.tfot.info/content/view/83/59/ Samsung's Hybrid Hard Drive Exposed] - An article and an interview with Andy Yang from Samsung about the future of hybrid drives
*ZDnet article, [http://news.zdnet.com/2100-9584_22-6121256.html Robson or hybrid hard drive? The battle is coming]
* [http://jasonkneen.blogspot.com/2007/11/hybrid-drives-and-vista-update.html Adding a Hybrid drive to a Vaio SZ1]

Hybrid RAM disk

* [http://reviews.cnet.co.uk/natelanxon/0,139102300,49292591,00.htm New hybrid hard disk has 1GB of RAM and its own CPU]
* [http://www.cs.fsu.edu/~awang/papers/tos2006.pdf The Conquest File System: Better Performance Through a Disk/Persistent-RAM Hybrid Design]
* [http://www.google.com/patents?id=aVZ4AAAAEBAJ&dq=hybrid+ram+disk Storage controller with the disk drive and the RAM in a hybrid architecture]
* [http://www.pcworld.com/article/id,136727-c,harddrives/article.html RAM Cache Speeds New Hybrid Hard Drive]