Niklas wrote:
> How many ide disks is it possible to use under linux, and how many is it
> "recommended" to use?
Currently, it's possible to use three ide controllers at once for a limit of
6 interfaces. This is a limit in the ide kernel code. Apparently, though,
expanding it should be easy. At least in a conversation I had with Andre,
the kernel udma guy, he said he could expand it to four or more, "but what
would be the point?".
Also, linux-software raid currently has a limit of 12 disks in a raid set.
I'm unsure how easy this limit would be to change, but there are ways around
this... making and using more than one raid set, or making a number of raid5
sets and then using those to make a striped array.
I have a system with 12 udma disks, and in practice it's been a nightmare.
Once you start using more than two interfaces the auto-tuning code in the
kernel ceases to work correctly, so you have to "tune up" each disk after
boot. Also, udma-66 has a cable length limit of 18", which can make it hard
to place disks. Consider as well if you can find a case that will allow you
to mount 14 disks, and if you can really route 14 ide cables inside it. 14"
cables will take up a LOT of space.
There is at least outboard ide raid5 -> scsi solution, that would allows you
to treat a raid5 set as a single scsi disk. Though this would be more
costly, it may save you a good number of hassles in the end. Otherwise I
would suggest making more than one box, and sticking 6-10 disks in each one.
You are right to plan on using one disk per interface. My 10 udma disk
raid5 set runs only slightly faster (accoring to bonnie) than access off of
any one of the disks in the set.
Good Luck,
Tom
