Raid Software Hardware difference?

Epidrive

I really wanted to know what's the difference between a Raid Software and a Raid Hardware in terms of its real use/purpose e.g. stripping, mirroring, etc.

Some say Raid Software is a bullacrap which i dont even know why.
And oh, my friend Google, is being useless.

HalfEatenPie

http://www.adaptec.com/nr/rdonlyres/14b2fd84-f7a0-4ac5-a07a-214123ea3dd6/0/4423_sw_hwraid_10.pdf

Google is still your friend?

Quote:

Benefit of Hardware Raid:

• Protected at boot: No negative impact on data availability
when boot drive has medium errors or fails completely.
• Performance independent of workload on server: Fast
memory, fast processor and no impact on the performance
of the application(s) running on the host system.
• RAID application independent of host: No data integrity
issues when system crashes.
• Enhanced protection in case of power loss: Hardware RAID
implementations typically keep track of in-progress writes
in non-volatile hardware. Software RAID implementations
lack this protection, which makes it difficult to recover from
a power loss during a write.
• Not vulnerable to viruses:RAID arrays are completely
independent of the host system and OS. No data integrity
issues occur if the host system fails.
• Offloads the RAID task from the host: Best suited for
complex RAID 5 or RAID 6 scenarios which usually offers
best cost/performance ratio.
• Dedicated GUI and software to build and maintain the
RAID: Easy setup and maintenance of the RAID array.
• Easy to migrate and replace: Card can be plugged in any
system and easily replaced or upgraded with the latest, best
performing variant. It is also easier to migrate from one
operating system to another.
• Supports advanced RAID features: Typical examples include
disk hot plug, array-level migration and online capacity
expansion.
• On-controller caching: Accelerates access times by usage of
cache memory including the ability to use write-back
caching if memory is protected by a battery.

Edit: What most people here measure is the I/O (or the Access Times), which a hardware raid card would improve in comparison to software raid.

Epidrive

@HalfEatenPie said: http://www.adaptec.com/nr/rdonlyres/14b2fd84-f7a0-4ac5-a07a-214123ea3dd6/0/4423_sw_hwraid_10.pdf

Google is still your friend?

Does that mean the raid software does not have those features?

Epidrive

Read your link. Thanks
It seems you can use google better than me.. I really had no luck finding the answer on google. Idk why.

HalfEatenPie

Yes. Basically. I mean basically if you skim the article (yeah I know its from adaptec, but it does make a point) you'll come to the Software Raid area. And this is what they wrote.

Benefits and drawbacks of “pure,” Operating System Software

RAID:
• Low cost: No extra charge for the RAID functionality, as it is
built into the OS. The only cost is the additional disk drives.

• Unprotected at boot (cannot manage or protect data at
  boot): Drive failure or corrupted data during boot and
  before the RAID software become active leads to an
  inoperable system.

• Additional performance load on server: System
  performance is impacted by the RAID application. The
  more drives involved and the more complex the RAID
  system is (e.g. involving parity on a RAID 5), the more
  impact on the overall performance. This solution is better
  suited for simple RAID 0, 1, 10 scenarios.

• Limited operating system migration:RAID functionality
  might be limited to the current OS. There is no way to
  migrate the array to other OSes or other versions of the
  same OS, if not all versions of the OS support RAID
  functionality).

• Vulnerable to viruses:Because RAID is running as an
  application on the computer system, viruses and other
  harmful software could impact RAID functionality.

• Data integrity issues due to system crashes: Software or
  hardware problems on the server can impact data
  consistency and integrity.

• Nowrite-back cache: Software RAID runs only in writethrough mode, but hardware RAID can run in write-back
  mode if it has a battery, adding another level of data
  protection. Write-back mode significantly enhances the
  write performance of a RAID array. There is no way to
  add a battery for software RAID.

Edit: In response to your second response, yeah basically hardware raid costs more, but is much more efficient and better in the long-run.

rm_

http://linux.yyz.us/why-software-raid.html

Why prefer Linux software RAID?

• Potential for increased hardware and software biodiversity
• Kernel engineers have much greater ability to diagnose and fix problems, as opposed to a closed source firmware. This has often been a problem in the past, with hardware RAID.
• Disk format is public
• ...thus, no vendor lock-in: Your data is not stored in a vendor-proprietary format.
• A controller-independent, vendor-neutral layout means disks can be easily moved between controllers. Sometimes a complete backup+restore is required even when moving between hardware RAID models from the same vendor.
• Eliminates single-points-of-failure (SPOF) compared to similar configurations of hardware RAID.
• RAID5 XOR runs on host CPU, which practically guarantees that it is far faster than most hardware RAID microcontrollers.
• RAID5 XOR speed increases as host CPU speeds increase.
• RAID speed increases as host CPU count (multi-thread, multi-core) increases, following current market trends.
• Cost. A CPU and memory upgrade is often cheaper and more effective than buying an expensive RAID card.
• Level of abstraction. Linux software RAID can distribute data across ATA, SCSI, iSCSI, SAN, network or any other block device. It is block device agnostic. Hardware RAID most likely cannot even span a single card.
• Hardware RAID has a field history of bad firmwares corrupting data, locking up, and otherwise behaving poorly under load. (certainly this is highly dependent on card model and firmware version)
• Hardware RAID firmwares have a very limited support lifetime. You cannot get firmware updates for older hardware. Sometimes the vendor even ceases to exist.
• Each hardware RAID has a different management interface, and level of feature support.
• Your hardware RAID featureset is largely locked in stone, at purchase time. With software RAID, the featureset grows with time, as new features are added to Linux... no hardware upgrade required.
• Additional RAID mode support. Most hardware controllers don't support RAID-6 as Linux software RAID does, and Linux will soon be adding RAID-5E and RAID-6E support.
• Error handling and logging varies from vendor to vendor (and card to card), with hardware RAID.
• Many ATA-based hardware RAID solutions either (a) fail to manage disk lifetimes via SMART, or (b) manage SMART diagnostics in a non-standard way.

Epidrive

@rm_ nice, thanks!

HalfEatenPie

Eh, @rm_ does bring up certain valid points, but personally I prefer hardware due to the above reasons.

Rallias

@Simple3x said: Some say Raid Software is a bullacrap which i dont even know why.

Only one kind of RAID copies the errors. It's not software.

jstapleton

I have Hardware raid on a number of machines servers and desktops and the performance is out of this world. software raid for me has never stepped up to the plate and lasted all of 20 minutes before i wiped the drives and did hardware raid.

Oliver

Probably should have waited more than 20 minutes. Generally takes longer than that to finish the first syncronisation/initialisation... :-P