HW vs SW RAID

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The difference between HW and SW RAID. The basic RAID knowledge.
SERVER STORAGE WHITE PAPER Hardware RAID VS Software RAID: Which Implementation is Best for my Application? ROM. Additionally, hardware-assisted software RAID usuall comes with a variety of drivers for the most popular operating RAID systems, and therefore, is more Os independent than pure software RAID HOST Benefits and Drawbacks of hybrid, Hardware-Assisted Software Hardware RAID can be found as an integral part of the solution RAID (e.g. integrated in the motherboard)or as an add-in card. If the Moderate cost: Only an hba (plug- in card or an necessary hardware is already integrated in the system solution, additional flash memory for the bios down on the then hardware RAID might become a software upgrade to your motherboard is needed; it may also include a hardware existing system. So like software RAID, hardware RAID might XOR accelerator if the controller supports raid 5 not be identified as such at first glance Protected at boot: No negative impact on data availability The simplest way to identify whether a solution is software or when boot drive has medium errors or fails completely hardware RAID is to read the technical specification or data Dedicated GUI and software to build and maintain the raid: sheet of the raid solution If the solution includes a Easy setup and maintenance of the RAId array microprocessor (usually called I/O processor, processor or Additional performance load on server Systems sometimes ROC- which means RAID on Chip), then is the performance is impacted by the raid application. The solution is a hardware RAID solution. If there is no processor, it more drives involved and the more complex the raid is a software raid solution system is(e. g involving parity on a RAID 5), the more This is important for your selection because of the system Impact on the overall performance. This solution is better suited for simple raid o, 1, 10 scenarios impacts of the software RAID VS hardware RAID implementation. These impacts include Limited operating system migration: RAID functionality is still dependent on the os as the driver runs on top of CPU utilization and performance when other applications the os. However, multiple drivers for a variety of oses are running do allow migration of the array to other OSes. This might Scalability of disk drives that can be added to a system be limited by the availability of a raid driver for very Ease of recovery after a data loss new OSes(e.g. newer versions of an OS might need a Capability for advanced data management/monitoring new raid driver -RAId drivers are more complex than Ability to manage disk drives consistently across diffcrcnt normal hBA driver programs, and therefore, it might take longer to develop them) Vulnerable to viruses: Because RAID is running as an Ability to add a battery backup option that allow to enable write caching on the controller to enhance write application on the computer system, viruses and other harmful software might impact RAID functionality performance of the system Data integrity issues duc to systcm crashes: Softwarc or Hardware RAID Implementations hardware problems on the server can impact data Hardware RAID can be implemented in a variety of ways: 1) consistency and integrity a discrete RAID Controller Card, or 2)as integrated hardware No write-back cache: Hardware-assisted software RAID based on RAlD)-on-Chip technology runs only in write-through mode, but hardware RAID D) Discrete RAID Controller Card can run in writc-back mode if it has a battery, adding another level of data protection. Write-back mode This is a plug-in expansion card that usually has a built-in RaID significantly enhances the write performance of a RAID processor(1/O processor and its own interfaces to the drives array There is no way to add a battery for hardware (I/O controllers). It usually plugs into PCI-X or PCle slots of the assisted software raid computer systems motherboard. Such plug-in cards are usually the most costly, but also the most flexible and best pcrforming Hardware RAID RAID Solutions. Here, the RAId functionality is completely A hardware raiD solution has its own processor and memory to independent of the host( computer system). The discrete run the raid application. In this implementation, the raid character of this card allows the usage of the highest performing system is an independent small computer system dedicated to T/O processor and fastest memory. The RAID card fully offloads the RAId application, offloading this task from the host system the task of creating a redundant storage subsystem from the computer system and does not impact the performance of the rest of the system, even in the case of a drive failure. more complex and space-efficient RAID levels(like RAID 5 or RAID 6 can be used without any impact on the system SERVER STORAGE WHITE PAPER Hardware RAID VS Software RAID: Which Implementation is Best for my Application? The additional i/o interfaces on the card usually allow for greater system expandability(adding more hard disk drives and Device driver more capacity). Even multiple Raid arrays do not impact the CI Express performance of the host system. These can easily be migrated to another operating system or even another host system or Host command olatform Abstraction Layer Benefits and Drawbacks of a discrete RaId Controller Card: Protected at boot: No negative impact on data availability RAID Stack RTOS plus when boot drive has medium errors or fails completely RAID Stack Performance independent of workload on server: Fast CHIM I/F(OSM) memory, fast processor and no impact on the performance SAS CHIM of the application(s) running on the host system RAID application independent of host: No data integrity Central Sequencer Central Sequencer issues when system crashes Microcode Enhanced protection in case of power loss: Hardware RAID implementations typically keep track of in-progress writes Link Sequencer n non-volatile hardware. Software RAID implementations Microcode Link Sequencer ck this protection, which makes it difficult to recover from a power loss during a write Benefits and Drawbacks of roc-based Hardware RAID Not vulnerable to viruses: RAID arrays are completely Protected at boot: No negative impact on data availability ndependent of the host system and Os. No data integrity when boot drive has medium errors or fails completely. issues occur if the host system fails RAID application independent of host: No data integrity Offloads the raid task from the host: Best suited for issues when system crashes complex raid 5 or rAid 6 scenarios which usually offers Not vulnerable to viruses: Raid array completely best cost/performance ratio ndependent of the host system and os. no data integrit Dedicated GUI and software to build and maintain the issues if host system fails RAID: Easy setup and maintenance of the raid array Enhanced protection in case of power loss: Hardware RAID Easy to migrate and replace: Card can be plugged in any implementations typically kcep track of in-progress writes system and easily replaced or upgraded with the latest, best in non-volatile hardware. Software RAID implementations performing variant. It is also casicr to migrate from onc lack this protection, which makes it difficult to recover from operating system to another. a power loss during a write Supports advanced RAID features: Typical examples include Offloads the raid task from the host: best suited for disk hot plug, array-level migration and online capacity complex raid 5 or raid 6 scenarios which usually offers expansion. best cost/ performance ratio On-controller caching: Accelerates access times by usage of Dedicated gui and software to build and maintain the cache memory including the ability to use write-back RAID: Easy setup and maintenance of the RAID array caching if memory is protected by a battery. Supports advanced RAID features: Typical examples include Highest cost: I/O processor and additional memory on a disk hot plug, array-level migration and online capacity plug-in card increases cost expansion 2)Integrated Hardware RAID solutions based on RAID-on- On-controller caching: Accelerates access times by usage of Chip(roc) technology cache memory including the ability to use write-back In ROC solutions, the RAId processor, memory controller, host caching if memory is protected by a battery interface, I/O interfaces for hard disk drive connection, and Medium cost: Lower chip count reduces cost and add sometimes even the memory, are all integrated into one single eliability compared to a discrete hardware rald chip. This chip can be integratcd into the motherboard and solution. Due to the high integration of an I/O processor offers hardware Raid capabilities with reduced cost(as just one, and I/O interfaces into one single chip, the clock highly integrated asiC, is needed frequency of these complex chips might be limited for now Next-generation roc solutions may overcome this The roc replaces the i/ interface chip you find on many server motherboards(e. g. a SCSI controller ch nip). That means that the Limited flexibility migration: RAID migration to other ROC solution integrates more than just the connectivity for the systems is only possible of they are equipped with a similar(compatible)RoC solution hard disk drives SERVER STORAGE WHITE PAPER Hardware RAID VS Software RAID: Which Implementation is Best for my Application? Is Hardware or Software rAid Best for your RAid attractive for such configurations Application? Features of the different raid implementations Now that we understand the benefits and drawbacks of the Features Pure Software Hardware-assisted HW RAID controller different RAID implementations, we can look at some typical RAID SW RAID ROC or add-in card server deployment scenarios and optimize the RaId subsystem Data protection Ye during boot to meet the overall server price performance goals Write-back caching No Pure Software RAID solutions: Entry-level rAid O or l for Enhanced protection N Yes performance or data availability is key. However, software RAID in case of power loss cannot be used on the boot drive as the operating system RAID RAID independent ofNo Yes functionality is not available until after the os boots host operating system RAID performance Depends on Depends on server High: Independent Targeted Applications: server load of server load 1. Workstations without large data storage requirements RAID functionalityYes ulnerable to viruses 2. Entry-level servers without boot protcction requirements Setup during bootNo Hybrid solutions: Cost-sensitive solutions similar to pure ility to migrate to No Limited other os versions software RAID, but with bootability requirements Typical RAID RAid 0. 1 RAID 0. 1 Advanced RAID applications RAid 5 or RAID 6 Targeted Applications 1. Entry-level servers without large storage requirements closing 2. Compute engines connected to networked storage This paper has shown the benefits that hardware RAID offers over software RAID implementations Hardware RAID solutions: Most feature-rich and highest performance solution. This may be implemented as RAID on the Advances in silicon technology are allowing for integration of the Motherboard (ROMB)or with plug-in cards to scale processors required for hardware Raid into single chip solutions performance and availability(e.g controller redundancy) and soon into commodity server chipsets, which will shrink the implementation cost. This reduced cost will enable a broader Targeted Applications: deployment of hardware RAID solutions into lower-priced 1. High Performance workstations with large data storage servers, making them available to more uscrs requirements Currently, new levels of data protection and manageability are 2. Entry level to enterprise servers requiring performance and available -raid 6 dual drive failure protection and data scalability from the storage subsystem encryption are two examples. In many cases, these hardware In general, hardware raid offers more advantages over RAID implementations can provide higher performance and software-based solutions for more complex raid algorithms lower cost solutions than external raid configurations Measurements indicate that for instance, software RAID-6 implementations impose a heavy load on system compute resources, especially in degraded mode. This makes hardware adaptec Adaptec, Inc. Literature Requests 691 South Milpitas Boulevar Us and canada:1(800442-7274or(403)957-7274 WorldWideWebhttp://www.adaptec.cam le:(408)9458600 Pre-Sales Support: US and Canada: 1(800)442-7274 or (408)957-7274 Fax(408)2622533 Pre-Sales Support: Europe: Tel: (44) 1276-854528 or Fax: (44)1276-854502 Copyright 2006 Adaptec, Inc. All rights reserved. Adaptec, the Adaptec logo, Snap Appliance, the Snap Appliance logc, Snap Server, Snap Disk, GuardianOS SnapOS, and Storage Manager are trademarks of daptec, Inc, which may be registered in some jurisdictions. Microsoft and Windows are registered trademarks of Microsoft Corporation, used under license. All other trademarks used are owned by their respec- tive owners Information supplied by Adaptec, Inc, is believed to be accurate and reliable at the time of printing, but Adaptec, Inc, assumes no responsibility for any errors that may appear in this document Adaptec, Inc, reserves the right, without notice, to make changes in product design or specifications. Information is subject to change without notice Printed in U.S.A. 03/06

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