[Discuss] PCI RAID card for Linux?

[David Bronaugh]

Alan W. Irwin wrote:
> On 2006-05-27 09:48-0700 Jim Roepcke wrote:
>
>> On 26-May-06, at 11:00 PM, David Bronaugh wrote:
>>
>>>> Do you have any recommendations for PCI RAID cards (or have a 
>>>> better idea?) that I can confidently use with Linux (and hopefully 
>>>> Dapper Drake)?  Hopefully something that isn't super-expensive, I 
>>>> definitely don't want to be spending hundreds but I honestly have 
>>>> no idea how much these kinds of cards cost.
>>>
>>> Don't bother with a RAID card, simply use both onboard IDE channels 
>>> and use Linux software RAID. It'll work fine.
>>
>> Excellent!
>>
>> IIRC, if I put an ATA hard drive on the same channel as the ATA 
>> CD-ROM drive the performance of the hard drive will suffer.  Is that 
>> true?  Should I be worried about that or is that just a myth/bunk?
>>
>
> Jim's question sparked an additional one of my own.  Additional problems
> with two disks are they generally cost more than one disk with the 
> same net
> storage capacity, require more power, generate more heat, etc. Linux
> software raid works at the partition level rather than disk level so
> RAIDing the partitions on a single device is certainly possible and 
> naively
> seems to deal with the two-disk problem Jim mentioned and the additional
> two-disk problems I mentioned.
It doesn't offer any gain, so no one does it. Plus it'll cause a seek 
storm every time you write, because the data will be in physically 
separated areas of the disk.

You don't even really gain anything in terms of the data corruption 
angle either, because RAID1 (mirroring) is not sufficient to detect 
which sector has failed, and which is valid. The same is true of RAID5.

What's best is the following: Have 2 disks. Put everything you care 
about on RAID1 (mirroring). Put temporary and replaceable data on RAID0 
(striping). This way you have the space you need to store wads of data, 
but also have the reliability you need to ensure you don't lose anything 
important.

David Bronaugh