port multiplication confusion!

[Tunnah]

Hello there folks I was wondering if someone with more of a brain than me (easy feat I assure you) could help me understand port multiplication.

I'm planning on building a media box for a house I'm about to move into. I currently run 6 HDs in my main rig but when I move into my new place I'm building a seperate rig with a low power setup (intel atom most probably) so my hard drives will have to be powered by a RAID card. The problem is 6 ports will cost me a fortune in cards so I'm looking into using a port multiplier.

But I'm having a bit of trouble figuring them out.
Can anyone point me in the right direction for a 2 port RAID card and the port multiplier that will work with it ? I'm wanting to run 10 drives total.

Or am I thinking of this the wrong way ? This port multiplier for instance confuses me. Does this need an eSata connection to split into 5 drives ? And what is the normal sata version ?

Sorry if this sounds noobish, for some reason I'm having a nightmare figuring this all out

EDIT: d'oh as soon as I posted this I found a really good tutorial. It's much simplier than I thought.

Now I just need varification: Would this port multiplier enable RAID with this card ?

My confusion now is does the port multiplier pass through RAID, or does it enable RAID if you have a none-RAID source ?

[blueball]

What RAID level are you looking to run?

NB it says on the manufacturer site that the Lycom card will

Work with PortMultiplier-aware SATA II Motherboard and LyCOM SATA II Host controllers like ST-124, ST-124NR, ST-125, ST-125NR, 64-105i, PE-100, PE-100N, PE-105N, PE-103, PE-103R5

Does your motherboard or RAID card support PMs?

[Steve]

Some chipsets don't support port multipliers properly: http://forums.anandtech.com/showthread.php?t=2080926 Intel ICH10 for example (I have a DAS box that I wanted to present as a JBOD which as effectively port-multiplier mode, but I have to use it in RAID mode as it will only see one disk).

A RAID card should, but with a cheap card like that I doubt the throughput will be up to much... it's a PCIe 1x card so you're trying to run a lot of disks down that one link.

We have some SAS cards that run a whole lot of disks even though they only have one SAS port (can run 4 SATA drives directly), but they connect to a SAS backplane and have an 8x slot, and that costs a fair bit more than a £40 RAID card.

It looks like the RR630 supports multipliers - there's no real difference between eSATA and SATA other than the cable and the tolerances on the signal so get whatever you need. The RAID card should see whatever disks are downstream for it, through the multiplier or otherwise, regardless of the number of ports it has - then you configure it however is appropriate.

Alternatively, why not get a couple of RAID cards, have more than one array, more resiliance, and more bandwidth?

[Tunnah]

blueball:
RAID5 utilizing 3tb disks
I later seen one of those cards it's £14 but I think I'd rather go for a highpoint.

Steve:
Throughput isn't an issue. This box will be a media box for my house that I live in with the missus, therefore the max draw will be 2 1080p streams. It's going to be setup WORM, I'll be using a seperate drive for all incoming data and moving them from there to the array over a 1gbit link, so basically at it's most punishing it'll be receiving a file at 110mb/s.

More RAID cards with more bandwidth etc. would be my first choice if I was doing anything mission critical.

Yeah I know about the intel issue, I wanted to run more than the 6 drives I have in my system (8 total but 1 SSD and 1 optical), luckily I found out before I went out and bought the multiplier ha.

Thanks for the info about seeing down the line, that clears it up perfectly I'll go for the none-RAID one. I dunno why I let this confuse me so much, mebbe having a stupid day.

What I'm planning to do atm is build a custom "case" that'll just be a stand for the mobo and walls with shelving to hold the drives, all sealed apart from fans with filters on. I'm starting with 10x3tb drives and maybe add another 10 down the line.

With it being a WORM setup I'm wondering if to just do RAID0 to maximize space, as it's usage is going to be incredibly low, is there any data yet on the reliability of the new 3tb drives ?

I use a seperate 2tb drive for my downloads so it gets punished a lot, and already has bad sectors. It's 13 months old but started showing errors about 4-5 months ago, would I be better using an SSD for downloads ?

[ChaosSystem]

I've used the port multiplier before. I was running software RAID under Linux and running a system with 10 drives. One of the problems was trying to figure out which drive was faulty. Another was a little known bug whereby the last drive would disappear while the system was in use.

[shaithis]

is there any data yet on the reliability of the new 3tb drives ?

It's a mechanical drive. Any reliability figures are pointless as it's the usual case of "a complete lottery".

[Tunnah]

ChaosSystem:
Damn that's a good point, I wonder if using a card that's designed to support port multipliers will help that issue. Hopefully the hardware RAID will stop the second issue too.

shaithis:
True, but I meant more in line with the higher densities being less reliable. I'm thinking maybe I will do RAID0 and just do monthly scans, these drives are going to be getting such low usage I should be able to deal with any potential failure before it becomes catastrophic

[mikerr]

True, but I meant more in line with the higher densities being less reliable. I'm thinking maybe I will do RAID0 and just do monthly scans, these drives are going to be getting such low usage I should be able to deal with any potential failure before it becomes catastrophic

Not all disk failures are gradual. I wouldn't rely on you having any warning in time to get any data off!

[Tunnah]

Well what I didn't realise is the level of sacrifice needed for RAID5, I thought on a 10 disk array I would need 2 disks, but 1 disk will do fine, so I reckon I will go for RAID5 after all

I'd rather lose 2.8tb (or whatever is it when formatted) than 28tb in case of sudden failure, forking out for an extra disk I can handle, but recovering that much space would create a nerdfit so big you could measure it on the richter scale

[ChaosSystem]

Look at RAID6 which would allow 2 drives to fail. Also look for a system whereby the failed drive can be identified. If you RAID5 the system, have a drive fail and then disconnect the incorrect drive, you basically failed 2 drives and you will lose the RAID.

[b0redom]

+1 for RAID-6. If one disk does fail, unless you have some sort of hardware controller, and even then with one, you're looking at a LONG rebuild time on an array that size.

10x 3TB is a LOT of storage for a residential array. It's what? 1000(ish) uncompressed BluRay rips.

I looked at large arrays before, but the problem is that you get into a situation where if any part of the system fails you need to be able to swap it out with an identical part, which is why I ended up going with FreeNAS on a microserver.

Do you really NEED that much storage? Can you rationalise it down into smaller blocks?

[Tunnah]

I'll deffo look into RAID-6. Yeah the space isn't overkill, in fact it won't be enough but it's going to take me so long to fill I'll just build another array when the time comes. I filled my 9tb array in <6 months and am now having to choose what to save.

I could split it down but I hate split volumes...retarded pet peeve but one none-the-less

From what I've been looking at, with the price of the RAID card and the 2 port multipliers, that's going to come to about £120-150, I'm wondering if to just buy this 8 port RAID card for £96 instead.

edit: Or Or this one that supports RAID6
I've got a few 8087 1-4 cables hanging around too, this way I've got direct RAID with no other components which could fail

[Tunnah]

If anyone was following looks like I've got my setup

This RAID card (rocketraid 2720GSL)

This SAS Expander, by HP

This will give me 32 drives and RAID6 for a touch over £300

[b0redom]

32 Drives on consumer hardware? You're mental!

[Tunnah]

Yeah I'm getting a lot of that haha. People hear this much hardware and they can't help but think there's some sort of mission critical work attached. It's just a very big media box, nothing more.

[b0redom]

It's not so much the quantity of hardware, it's the way you're setting it up. A 32 disk single RAID array on something without a meaty CPU to rebuild it if a disk fails is just asking for trouble. You'll probably be fine for 99% of the time, but that 1% could cause you a whole world of pain.

Then again I really can't see the need for a 64TB RAID array in a domestic setting anyway. Are you planning on running your own full feed NNTP server or something? The power draw from the disks alone is going to be mighty expensive.