Re: 2003 OS Server Hard drive install limit.
From: Frank McCallister (anonymous)
Date: 06/23/04
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Date: Wed, 23 Jun 2004 17:44:33 -0500
Well all I can say is that in 20 years of doing this stuff I have never had
a Hardware Raid problem I wasn't able to recover from. The closest I have
come have always been my boneheaded errors :-( On the other hand I have seen
enough horror stories on the forums about people not being able to boot a
software Raid beacause of the boot drive or other softwaare issues that I
wouldn't touch it. You save a few dollars on your servers, I won't on mine!
I just pray that the people who do have really good backups.
Frank
"root" <postmaster@buchanangc.com> wrote in message
news:uyPfkEWWEHA.2168@TK2MSFTNGP10.phx.gbl...
>
> "Frank McCallister" <anonymous> wrote in message
> news:eT68hxVWEHA.2576@TK2MSFTNGP10.phx.gbl...
>> Opinions! From Whitepaper on subject:
>> http://www.zzyzx.com/products/whitepapers/pdf/hard_vs_soft_raid.pdf
>
> The above is a company selling HW RAID. All the information in the above
> .pdf can be assumed to be marketing drivel targetted towards their bottom
> line $.
>
>> To make informed disk array purchase decisions, it is important to look
>> beyond a discussion of
>>
>> the different RAID levels and also understand the differences between
>> software and hardwarebased
>>
>> RAID implementations. Software-based arrays are typically the least
>> expensive to
>>
>> implement. Conversely, the true cost of this implementation can increase
>> dramatically if the
>>
>> demand they place on the server CPU necessitates an upgrade to maintain
>> acceptable network
>
>
> SW RAID 1 places almost no demand on the CPU.
>
>> performance.
>>
>> Software & Hardware RAID Defined
>>
>> Software-based RAID implementations are either operating system-based, or
>> they are application
>>
>> programs that run on the server. Most operating system RAID
> implementations
>> provide support
>>
>> for RAID-1, and to a lesser degree, some operating systems also provide
>> support for RAID-5. All
>>
>> array operations and management functions are controlled by the array
>> software running on the
>>
>> host CPU. Most hardware-based arrays are implemented directly on a
>> host-based RAID adapter
>>
>> and tightly couples the array functions with the disk interface.
>> Additionally, this design allows all of
>>
>> the array operations and management to be off-loaded from the host CPU
>> and
>> instead, be
>
> There is nothing to offload for RAID 1 except during a rebuild.
>
>> executed locally on an embedded-processor. Different hardware RAID
> adapters
>> offer some
>>
>> combination of RAID configuration support options including RAID-0,
> RAID-1,
>> RAID-3, and RAID-
>>
>> 5.
>>
>> Performance Differences in Hardware & Software RAID
>>
>> Just like any other application, software-based arrays occupy host system
>> memory, consume
>
> There is a very small memory footprint for SW RAID 1.
>
>> CPU cycles and are operating system dependent. By contending with other
>> applications that are
>>
>> running concurrently for host CPU cycles and memory, software-based
>> arrays
>> degrade overall
>
> True for RAID 5 but NOT TRUE for RAID 1.
>
>> server performance. Also, unlike hardware-based arrays, the performance
>> of
> a
>> software-based
>>
>> array is directly dependent on server CPU performance and load.
>
> True for RAID 5 but not for RAID 1.
>
>> Except for the array functionality, hardware-based RAID schemes have very
>> little in common with
>>
>> software-based implementations. Since the host CPU can execute user
>> applications while the
>>
>> array adapter's processor simultaneously executes the array functions,
>> the
>> result is true hardware
>>
>> multi-tasking. Hardware arrays also do not occupy any host system memory,
>> nor are they
>>
>> operating system dependent. Hardware arrays are also highly fault
> tolerant.
>
> They are no more fault tolerant than SW RAID 1 and in fact the addition of
> a
> complex HW RAID controller actually decreases overall system reliability
> over intrinsic SW RAID 1.
>
>> Since the array logic
>>
>> is based in hardware, software is NOT required to boot. Some software
>> arrays, however, will fail
>>
>> to boot if the boot drive in the array fails. For example, an array
>> implemented in software can only
>>
>> be functional when the array software has been read from the disks and is
>> memory-resident.
>
> Double talk.
>
>> What happens if the server can't load the array software because the disk
>> that contains the fault
>>
>> tolerant software has failed? Software-based implementations commonly
>> require a separate boot
>
> That's flat false for intrinsic SW RAID 1.
>
>
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- In reply to: root: "Re: 2003 OS Server Hard drive install limit."
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