Rant P35 ich9r raid controller and large volumes

[TdC]

Hi guys,

just thought I'd give you a heads-up regarding the (popular) ich9r raid controller in use on many P35 based mobos. Well, recently I managed to get my hands on 4 750GB spinpoints, so I made a backup, removed my two 250GB disks that's I'd been running as a mirror, fit the 4 Spinpoints and turned on my desktop.

After entering the intel RAID setup with ctrl-i, all the disks were visible, and I was free to set up whatever volume I wanted so I added the 4 disks into a raid 5 setup with default stripe width and maximum size. Booting off my Vista64 Ultimate dvd, I experienced a twang of concern as Vista refused to see the created volume for reasons as yet unknown. I tried to have Vista setup load the raid chip's driver off an USB stick to no avail, the volume remained invisible. I couldn't remember that from when I installed onto the mirror. In fact, I remembered that Vista saw the mirror right away and didn't need any fancy schmancy driver loading.

Mucking about in my BIOS, I turned the intel and sis raid chips off and on, tried different combinations of AHCI, RAID, etc to no avail. Nothing worked, and in the intel RAID setup, I could do everything so it was working and all, the damn thing just wouldn't become visible. After a while the thought struck me that perhaps I should try a smaller volume size than the maximum offered, so I did and hey presto, a bootable volume! Fiddling about with sizes, I discovered that the ich9r will *not* allow a bootable volume that >=2048GB. being me, I didn't do any research beforehand to see if there were any limitations at the chip level, so I made a boot volume of 250GB and put the remainder in another one, and woah! Vista install saw both of them,and no extra drivers or anything! BIOS was set to the intel chip configured to RAID and the sis chip to IDE. All is well, and the RAID delivers around 180MB/s. I'll see if it gets any faster once Vista's updated itself and stuffs.

 

[nath]

Being a bit of a RAID novice, does Raid 5 just do striping or is it the one that does parity checking too?

Also, what's the deal if one of the drives fails? You can't just take out the drives and pop them in another machine to recover the data can you? Do you just need to be really thorough about keeping your data safe or are there other things you can do if things screw up/vista fails/whatever?

 

[TdC]

RAID5 is a parity stripe, ie a bunch of disks together that can survive the loss of one of the set. The formula is N-1, as the size of one disk of the set will be used by the parity, but all disks participate in the N as the parity is spread over all members.

A regular stripe (RAID0), ie without parity, offers the best performance but can not survive the loss of one of it's members.

So, as you see it's usually a trade-off between speed, space and redundancy and imo RAID5 is the most useful combination of 3 or more disks with that in mind.

If a member disk fails, you remove it and replace with the same sized (or larger) model and the RAID controller will rebuild the array for you until it is back in normal state. With one disk gone, the array will be in degraded state. It will still function, but it will no longer have redundancy unless you're using a fancy controller with hotspare disks and that kind of stuff.

the other stuff you can do is just make regular backups. I mean, dvd's are cheap.

 

[nath]

If vista fails but all the disks remain ok, what are your options then (apart from over-installing). Would an Ubuntu live disk or something similar read the data OK as long as the RAID is still configured and working?

 

[TdC]

sure. if your linux has a driver for the ich9r chip it will just see a disk and the disk will behave like a disk. your livecd will be able to mount the volumes and everything as long as it knows about ntfs.

 

[nath]

Cool, good stuff to know

 

[TdC]

ofc it will be a good idea to check your preferred OS's hardware compatibility list, and perhaps browse the web for success stories and best practices and stuff.

 

[Gahn]

Actually with 4 Disks you could run a Raid 1+0 which gives best speed performance and full redundacy.
If you got speed performance problems Raid 5 isn't the best solution, it surely is the most secure one for Data Protection tho.

 

[TdC]

a striped mirror will only guard against two disks breaking if they're kind enough to break one on each side of the mirror though, and I'm not entirely sure about the speed, but I'll certainly take your word for it. I mentioned the speed/space/redundancy tradeoff, and in this case the use of raid 5 leaves me with 2.25Tb, whereas I'd have had 1.5Tb if I'd done the 0+1 route, the difference being another disk. I'm such a cheapskate lol

I may be tempted to give it a bit of a test if I am still fit and frisky when I get off the train later this evening, but currently I think I'll be fine.

 

[Gahn]

a striped mirror will only guard against two disks breaking if they're kind enough to break one on each side of the mirror though, and I'm not entirely sure about the speed, but I'll certainly take your word for it. I mentioned the speed/space/redundancy tradeoff, and in this case the use of raid 5 leaves me with 2.25Tb, whereas I'd have had 1.5Tb if I'd done the 0+1 route, the difference being another disk. I'm such a cheapskate lol

I may be tempted to give it a bit of a test if I am still fit and frisky when I get off the train later this evening, but currently I think I'll be fine.

Eheh well if you turn to be unlucky you could cook 2 disks on Raid 5 also and your system will become unstable (that's y you normally do it with 5 disk [1 spare]) ^^

 

[TdC]

haha if I am that unlucky having a bad RAID will probably be the least of my worries

 

[Kryten]

Aye, I'd read that previously (the 2tb bootable partition limit). This issue is solved on the ICH10R chipsets on the P45 motherboards replacing the 35's.

5 x 400gb units in this system at the moment so just shy of that issue

 

[TdC]

hehe aye. typical of me to dive in without reading up properly only took me two hours of swearing to twig what was up

ooh and welcome to the house of Mod, Kryt! Haven't seen that title on you yet

 

[Kryten]

Heh, cheers been a couple of weeks - spend so much time on this forum anyway it sort of makes sense
Saves me hassling Jonty so much too - we make a good team

 

[Gahn]

Heh, cheers been a couple of weeks - spend so much time on this forum anyway it sort of makes sense
Saves me hassling Jonty so much too - we make a good team

Gibf the anti banzor umbrella

 

[Chilly]

so hold on, is this vista being shit or the chipset?

 

[TdC]

no, it's the chipset. the 9 won't allow bootable volumes over 2TB

 

[inactionman]

In an enterprise environment I've always recommended RAID 5 + a hot standby disk, so if a disk fails the array is rebuilt automatically ASAP, but that's probably not feasible with a consumer chipset.

There's lots of other considerations with RAID-5, like making sure your disks come from different batch numbers (to ensure you don't get all your disks from a duff batch), etc.

RAID-6 is becoming popular these days, and does the job of RAID-5 + hotstandby (and gives more usable space), but it requires you lose 2 disks to parity, although it does make larger arrays more practical.

All this is becoming less of an issue in these days of SAN/NAS though, you let the appliances do all the work!

 

[TdC]

I'll see if it gets any faster once Vista's updated itself and stuffs.

Vista has now updated itself with SP1 and all that jazz, and, if anything the RAID has gotten slightly slower. HDtach now averages at around 175MB/s on the big (2tb) volume and 180MB/s on the boot volume (250gb).

 

[Kryten]

I've noticed a small decrease in drive performance myself on the same chipset & similar RAID configuration. Not sure what's doing it, have just been keeping an eye. I'm personally suspicious of an update other than SP1, will be going through them all later this week to try and weed out the suspects.

 

[TdC]

not that I'm really complaining mine you: 175MB/s is still well over three times faster than the older 250gb drives I had in a mirror configuration!