-----Original Message-----
From: David Schwartz <[EMAIL PROTECTED]>
To: Adam Snodgrass <[EMAIL PROTECTED]>; [EMAIL PROTECTED]
<[EMAIL PROTECTED]>
Cc: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Tuesday, 29 December, 1998 17:11
Subject: RE: Hardware RAID
> While Adam's comments are certainly correct, they are also just one side
of
>a coin. One could equally well argue that hardware raid solutions are not
as
>fault tolerant since typically a single controller failure knocks out the
>entire array and this is not necessarily true for software raid.
Quite true. But, I think the likelyhood of a drive failure to be greater
than a controller failure (fewer moving parts). About the same either way
you go.
> As for RAM dedicated specifically to your array, you pretty much need to
do
>this even in a hardware raid situation. Otherwise, the I/O traffic across
>the disk controller would seriously hamper performance. So I think that's a
>non-argument. Besides, RAM is so cheap that this shouldn't be an issue.
When I mentioned the RAM, I definitely agree with having memory on the
controller itself (so far I've found *no* RAID controllers that will operate
sans cache) is a must. My point was more towards the cpu/memory usage
software RAID would need, and thus disallow my other server processes from
having. Not having any experience with Linux's software RAID driver, I
couldn't hope to guess what type of memory footprint it might take. My
point could be thus rendered moot were the resources needed not extravagant.
> It will usually take more CPU to handle software raid than hardware raid,
>but that's easily solved by using a more powerful CPU. The specifics of
this
>equation depend upon many factors.
For me, I am happier with the idea of having a processor and memory
dedicated to handling my array. I am certainly not knocking on Linux's
software RAID driver; very probably I will setup such an array on my home
machine to avoid the high cost of a RAID controller. :)
> Whether the I/O load to/from the CPU is higher or not depends upon many
>factors. Generally, for mirroring, hardware raid is better (since software
>raid doubles the I/O required). For striping, it's about the same either
>way.
Mirroring is my explicit goal for the machines I will be implementing RAID.
None of them currently take large amounts of disk I/O; I simply want to get
some rock solid fault tolerance for my data.
> As for the boot/load the system issue, even many people who use hardware
>raid don't put their boot partitions on the raid array. With Linux, you can
>boot from floppy anyway.
Which issues would booting from the array bring up? This is something I'll
have to take into consideration certainly.
> I'm not saying that software raid is better than hardware raid. Generally,
>my experience has been that the reverse is true. Just that it's usually a
>very close call.
I think I'd agree; I'm just inclined towards a hardware solution. My more
specific queries are which controller will work the best for my situation.
Thanks for the input. :)
> DS
Regards,
Adam Snodgrass
