Hybrid drive

From Wikipedia, the free encyclopedia

Jump to: navigation, search
This article is about the computer hard disk. For the automobile propulsion system, see Hybrid Synergy Drive.
 This article is in need of attention from an expert on the subject. WikiProject Computing or the Computing Portal may be able to help recruit one. (April 2009)
The neutrality of this article is disputed. Please see the discussion on the talk page. Please do not remove this message until the dispute is resolved. (January 2008)
This article needs additional citations for verification. Please help improve this article by adding reliable references (ideally, using inline citations). Unsourced material may be challenged and removed. (February 2007)

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,[1] decreased power consumption, and improved reliability.

Samsung released the first hybrid drives, primarily for notebook computers, to OEMs in March 2007.[2]

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 11%.[3] Microsoft uses the name ReadyDrive to describe the software side of this technology.[4] While hybrid drives are not required for Vista Premium certification of laptops, some confusion arose as to whether such drives would be mandatory.[5]

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.

Contents

[edit] 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 shutting 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.[citation needed]

Early estimates place the actual hard drive usage (when the platters are spinning) at anywhere between 1.25%[6] and 10%[7] 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.

[edit] Claimed benefits

 This section needs additional citations for verification. Please help improve this article by adding reliable references (ideally, using inline citations). Unsourced material may be challenged and removed. (July 2007)

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 do not need to spin as much, power consumed by the hard drive and dissipated as heat is less than non-hybrid drives. For mobile computers this extends battery life between 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.

[edit] Claimed drawbacks

There are some inherent drawbacks to the use of hybrid drives:[8][9][10]

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.[9]
Increased cost
Hybrid hard drives are currently more expensive than their non-hybrid counterparts, because of the higher cost of flash memory.[9]
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.[8] 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.[8][11]
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.

[edit] Software implementation

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

Hybrid drives may also be implemented in software, using other memory instead of a buffer built into the hard drive.[dubious – discuss] Examples of such systems include the SuperCache-II cacheing software (implements hybrid RAM drive), and Windows Vista ReadyBoost, which uses separate flash memory and hard disk to make a hybrid drive. Performance of the combined drive may be affected by the speed of the CPU and speed of the separate memory used, in addition to the speed of the hard drive interface.

[edit] 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. If 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.

Battery backup allows data to be written to permanent storage when the device is shut down,[12] and may allow data retention in RAM for limited periods.

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.

[edit] See also

[edit] References

  1. ^ "Samsung says flash drive boosts speed of Windows Vista". Electronics Weekly. 26 July 2006. http://www.electronicsweekly.com/Articles/2006/07/26/39320/Samsung+says+flash+drive+boosts+speed+of+Windows+Vista.htm. Retrieved on 2006-01-21. 
  2. ^ Ricker, Thomas (2007-03-07). "Samsung's Hybrid Hard Drive (HHD) released to OEMs". Engadget. http://www.engadget.com/2007/03/07/samsungs-hybrid-hard-drive-hhd-released-to-oems/. Retrieved on 2007-04-25. 
  3. ^ dvnation.com
  4. ^ skymonkey.org
  5. ^ Fischer, Ken (2006-06-14). "Hybrid hard drives are not a Vista Premium requirement". One Microsoft Way (Ars Technica). http://arstechnica.com/journals/microsoft.ars/2006/6/14/4328. Retrieved on 2008-02-16. 
  6. ^ Kanellos, Michael "Hybrid drive to extend notebook battery life" CNET News.com 26.04.2005
  7. ^ "Notebook Storage Gets Buffer" Maximum PC July 2005, pg. 15
  8. ^ a b c skymonkey: what are hybrid hard drives (HHDs)?
  9. ^ a b c Hybrid drives: not so fast!
  10. ^ A. Birrell, M. Isard, C. Thacker, T. Wobber. A Design for High-Performance Flash Disks In Operating Systems Review, 41(2), April 2007, pages 88-93.
  11. ^ StorageReview: Continuous Power vs. Peak Power at Spin-Up
  12. ^ Platinum HDD - combining the harddrive with a DRAM | NordicHardware

[edit] External links

Hybrid RAM disk

Retrieved from "http://en.wikipedia.org/wiki/Hybrid_drive"
Personal tools