FS12-NV7 – Frank Leonhardt's Blog

Del FS12-NV7 and other 2U server (e.g. C6100) disk system hacking

(Photographs to follow)

A while back I reviewed the Dell FS12-NV7 – a 2U rack server being sold cheap by all and sundry. It’s a powerful box, even by modern standards, but one of its big drawbacks is the disk system it comes with. But it needn’t be.

There are two viable solutions, depending on what you want to do. You can make use of the SAS backplane, using SAS and/or SATA drives, or you can go for fewer SATA drives and free up one or more PCIe slots as Plan B. You probably have an FS12 because it looks good for building a drive array (or even FreeNAS) so I’ll deal with Plan A first.

Like most Dell servers, this comes with a Dell PERC RAID SAS controller – a PERC6/i to be precise. This ‘I’ means it has internal connectors; the /E is the same but its sockets are external.

The PERC connects to a twelve-slot backplane forming a drive array at the front of the box. More on the backplane later; it’s the PERCs you need to worry about.

The PERC6 is actually an LSI Megaraid 1078 card, which is just the thing you need if you’re running an operating system like Windows that doesn’t support a volume manager, striping and other grown-up stuff. Or if your OS does have these features, but you just don’t trust it. If you are running such an OS you may as well stick to the PERC6, and good luck to you. If you’re using BSD (including FreeNAS), Solaris or a Linux distribution that handles disk arrays, read on. The PERC6 is a solution to a problem you probably don’t have, but in all other respects its a turkey. You really want a straightforward HBA (Host Bus Adapter) that allows your clever operating system to talk directly with the drives.

Any SAS card based on the 1078 (such as the PERC6) is likely to have problems with drives larger than 2Tb. I’m not completely sure why, but I suspect it only applies to SATA. Unfortunately I don’t have any very large SAS drives to test this theory. A 2Tb limit isn’t really such a problem when you’re talking about a high performance array, as lots of small drives are a better option anyway. But it does matter if you’re building a very large datastore and don’t mind slower access and very significant resilvering times when you replace a drive. And for large datastores, very large SATA drives save you a whole lot of cash. The best capacity/cost ratio is for 5Gb SATA drives

Some Dell PERCs can be re-flashed with LSI firmware and used as a normal HBA. Unfortunately the PERC6 isn’t one of them. I believe the PERC6/R can be, but those I’ve seen in a FS12 are just a bit too old. So the first thing you’ll need to do is dump them in the recycling or try and sell them on eBay.

There are actually two PERC6 cards in most machine, and they each support eight SAS channels through two SFF-8484 connectors on each card. Given there are twelve drives slots, one of the PERCs is only half used. Sometimes they have a cable going off to a battery located near the fans. This is used in a desperate attempt to keep the data in the card’s cache safe in order to avoid write holes corrupting NTFS during a power failure, although the data on the on-drive caches won’t be so lucky. If you’re using a file system like that, make sure you have a UPS for the whole lot.

But we’re going to put the PERCs out of our misery and replace them with some nice new LSI HBAs that will do our operating system’s bidding and let it talk to the drives as it knows best. But which to pick? First we need to know what we’re connecting.

Moving to the front of the case there are twelve metal drive slots with a backplane behind. Dell makes machines with either backplanes or expanders. A backplane has a 1:1 SAS channel to drive connection; an expander takes one SAS channel and multiplexes it to (usually) four drives. You could always swap the blackplane with an expander, but I like the 1:1 nature of a backplane. It’s faster, especially if you’re configured as an array. And besides, we don’t want to spend more money than we need to, otherwise we wouldn’t be hot-rodding a cheap 2U server in the first place – expanders are expensive. Bizarrely, HBAs are cheap in comparison. So we need twelve channels of SAS that will connect to the sockets on the backplane.

The HBA you will probably want to go with is an LSI, as these have great OS support. Other cards are available, but check that the drivers are also available. The obvious choice for SAS aficionados is the LSI 9211-8i, which has eight internal channels. This is based on an LSI 2000 series chip, the 2008, which is the de-facto standard. There’s also four-channel -4i version, so you could get your twelve channels using one of each – but the price difference is small these days, so you might as well go for two -8i cards. If you want cheaper there are 1068-based equivalent cards, and these work just fine at about half the price. They probably won’t work with larger disks, only operate at 3Gb and the original SAS standard. However, the 2000 series is only about £25 extra and gives you more options for the future. A good investment. Conversely, the latest 3000 series cards can do some extra stuff (particularly to do with active cables) but I can’t see any great advantage in paying megabucks for one unless you’re going really high-end – in which case the NV12 isn’t the box for you anyway. And you’d need some very fast drives and a faster backplane to see any speed advantage. And probably a new motherboard….

Whether the 6Gb SAS2 of the 9211-8i is any use on the backplane, which was designed for 3Gb, I don’t know. If it matters that much to you you probably need to spend a lot more money. A drive array with a direct 3Gb to each drive is going to shift fast enough for most purposes.

Once you have removed the PERCs and plugged in your modern-ish 9211 HBAs, your next problem is going to be the cable. Both the PERCs and the backplane have SFF-8484 multi-lane connectors, which you might not recognise. SAS is a point-to-point system, the same as SATA, and a multi-lane cable is simply four single cables in a bundle with one plug. (Newer versions of SAS have more). SFF-8484 multi-lane connectors are somewhat rare, (but unfortunately this doesn’t make them valuable if you were hoping to flog them on eBay). The world switched quickly to the SFF-8087 for multi-lane SAS. The signals are electrically the same, but the connector is not.

So there are two snags with this backplane. Firstly it’s designed to work with PERC controllers; secondly it has the old SFF-8484 connectors on the back, and any SAS cables you find are likely to have SFF-8087.

First things first – there is actually a jumper on the backplane to tell it whether it’s talking to a PERC or a standard LSI HBA. All you need to do is find it and change it. Fortunately there are very few jumpers to choose from (i.e. two), and you know the link is already in the wrong place. So try them one at a time until it works. The one you want may be labelled J15, but I wouldn’t like to say this was the same on every variant.

Second problem: the cable. You can get cables with an SFF-8087 on one end and an SFF-8484 on the other. These should work. But they’re usually rather expensive. If you want to make your own, it’s a PITA but at least you have the connectors already (assuming you didn’t bin the ones on the PERC cables).

I don’t know what committee designed SAS cable connectors, but ease of construction wasn’t foremost in their collective minds. You’re basically soldering twisted pair to a tiny PCB. This is mechanically rubbish, of course, as the slightest force on the cable will lift the track. Therefore its usual to cover the whole joint in solidified gunk (technical term) to protect it. Rewiring SAS connectors is definitely not easy.

I’ve tried various ways of soldering to them, none of which were satisfactory or rewarding. One method is to clip the all bare wires you wish to solder using something like a bulldog clip so they’re at lined up horizontally and then press then adjust the clamp so they’re gently pressed to the tracks on the board, making final adjustments with a strong magnifying glass and a fine tweezers. You can then either solder them with a fine temperature-controlled iron, or have pre-coated the pads with solder paste and flash across it with an SMD rework station. I’d love to know how they’re actually manufactured – using a precision jig I assume.

The “easy” way is to avoid soldering the connectors at all; simply cut existing cables in half and join one to the other. I’ve used prototyping matrix board for this. Strip and twist the conductors, push them through a hole and solder. This keeps things compact but manageable. We’re dealing with twisted pair here, so maintain the twists as close as possible to the board – it actually works quite well.

However, I’ve now found a reasonably-priced source of the appropriate cable so I don’t do this any more. Contact me if you need some in the UK.

So all that remains is to plug your HBAs to the backplane, shove in some drives and you’re away. If you’re at this stage, it “just works”. The access lights for all the drives do their thing as they should. The only mystery is how you can get the ident LED to come on; this may be controlled by the PERC when it detects a failure using the so-called sideband channel, or it may be operated by the electronics on the backplane. It’s workings are, I’m afraid, something of a mystery still – it’s got too much electronics on board to be a completely passive backplane.

Plan B: SATA

If you plan to use only SATA drives, especially if you don’t intend using more than six, it makes little sense to bother with SAS at all. The Gigabyte motherboard comes with half a dozen perfectly good 3Gb SATA channels, and if you need more you can always put another controller in a PCIe slot, or even USB. The advantages are lower cost and you get to free up two PCIe slots for more interesting things.

The down-side is that you can’t use the SAS backplane, but you can still use the mounting bays.

Removing the backplane looks tricky, but it really isn’t when you look a bit closer. Take out the fans first (held in place by rubber blocks), undo a couple of screws and it just lifts and slides out. You can then slot and lock in the drives and connect the SATA connectors directly to the back of the drives. You could even slide them out again without opening the case, as long as the cable was long enough and you manually detached the cable it when it was withdrawn. And let’s face it – drives are likely to last for years so even with half a dozen it’s not that great a hardship to open the case occasionally.

Next comes power. The PSU has a special connector for the backplane and two standard SATA power plugs. You could split these three ways using an adapter, but if you have a lot of drives you might want to re-wire the cables going to the backplane plug. It can definitely power twelve drives.

And that’s almost all there is to it. Unfortunately the main fans are connected to the backplane, which you’ve just removed. You can power them from an adapter on the drive power cables, but there are unused fan connectors on the motherboard. I’m doing a bit more research on cooling options, but this approach has promising possibilities for noise reduction.

21-September-1721-September-17

Dell FS12-NV7 Review – Bargain FreeBSD/ZFS box

It seems just about everyone selling refurbished data centre kit has a load of Dell FS12-NV7’s to flog. Dell FS-what? You won’t find them in the Dell catalogue, that’s for sure. They look a bit like C2100s of some vintage, and they have a lot in common. But on closer inspection they’re obviously a “special” for an important customer. Given the number of them knocking around, it’s obviously a customer with big data, centres stuffed full of servers with a lot of processing to do. Here’s a hint: It’s not Google or Amazon.

So, should you be buying a weirdo box with no documentation whatsoever? I’d say yes, definitely. If you’re interests are anything like mine. In a 2U box you can get twin 4-core CPUs and 64Gb of RAM for £150 or less. What’s not to like? Ah yes, the complete lack of documentation.

Over the next few weeks I intend to cover that. And to start off this is my first PC review for nearly twenty years.

So the Dell FS12-NV7:

FS-12 looking at the back panel. Note the cowling across the CPUs

As I mentioned, it’s a 2U full length heavy metal box on rails. On the back there are the usual I/O ports: a 9-way RS-232, VGA, two 1Gb Ethernet, two USB2 and a PS/2 keyboard and mouse. The front is taken up by twelve 3.5″ hard drive bays, with the status lights and power button on one of the mounting ears to make room. Unlike other Dell servers, all the connections are on the back, only.

If you want to play with the metalwork, the rear panel is modular and can easily be unscrewed although in practice there’s not much scope for enhancement without changing the motherboard.

Speaking of metalwork, it comes with a single 1U PSU. There’s space above it for a second, but the back panel behind the PSU bay would need swapping – or removing – if you wanted to add a second. The area above the existing unit is just about the only space left in the box, and I have thought of piling up a load of 2.5″ drives there.

Taking the top off is where the fun starts. Inside there’s large Gigabyte EATX motherboard – a Gigabyte GA-3CESL-RH. All the ones I’ve seen are rev 1.7, which is a custom version but its similar to a rev 1.4. It does have, of all things, a floppy disk controller and an IDE (PATA) connector. More generally usefully, there are two more USB headers, a second RS-232 and six SATA sockets (3Gb). At the back there’s either a BMC module, or a socket where it used to be. If you like DRAC, knock yourself out (you’re likely to be barely concious to begin with). Seriously, this is old DRAC and probably only works with IE 2.0 or something. (You can probably tell I haven’t bothered to try it). The BIOS also allows you to redirect the console to the serial port for remote starting.

The Ethernet ports are Marvel 88E1116 1Gb, and haven’t given me any trouble. The firmware supports PXE, and I’m pleased to say that WoL works with the FreeBSD drives.

Unfortunately, while the original Gigabyte model sported twin PCI and three PCIe sockets, the connectors are missing from these examples. It’s hard to find anything with a bit of grunt that can also use with your old but interesting PCI cards. It should be possible to rework it by adding the sockets and smoothing caps and sockets; fortunately the SMD decoupling caps are already still there. On the other had, you could find another motherboard with PCI sockets if that’s what you really want.

But grunt is what this box is all about, and there’s plenty of that.

This is board was designed for Opteron Socket-F processors; specifically the 2000 series (Barcelona and Shanghi). The first digit refers to the number of physical CPUs that work together (either 2 or 8), the second is a code for the number of cores (1=1, 2=2, 3=4, 4=6, 5=8). The last two digits are a speed code. It’s not the frequency, it’s the benchmark speed. I’ve heard rumours that some of FS-12s contain six-core CPUs, but I’ve only seen the 2373EE myself. The EE is the low power consumption version. Sweet.

If I could choose any Opeteron Socket-F CPU, the 2373EE is almost as good as it gets. It’s a tad slower than some of the other models running at 2.1GHz , but has significantly lower power and cooling requirements and was one of the last they produced in the 45nm process. It would be possible to change it for a 2.3GHz version, or one with six cores, but otherwise pretty much every other Opteron would be a downgrade. In other words, don’t think you can hot-rod it with a faster processor – you’re unlikely to find a Socket-F CPU anyway. After these, AMD switched to the Bulldozer line in an AM3+ socket.

This isn’t to say the CPU is modern. It does have the AMD virtualisation instructions, so it’s good news if you want to run nested 64-bit operating systems or hypervisors. The thing it lacks that I’d like most are the AES instructions that appeared in Bulldozer onwards. If you’re doing a lot of crypto, this matters. If you’re not, it doesn’t. Naturally, it implements the AMD64 instruction set, as now used by Intel, and all the media processing bit-twiddle stuff if you can use it. AMD has traditionally been at the forefront of processing smarter, whereas Intel goes for brute force and cranks up the clock speed. This is why AMD has, in my opinion, made assembler programming fun again.

Eight very capable Opteron cores: a good start. This generation supported DDR2 ECC RAM, and these boxes have 16 sockets (eight per CPU). They should be able to support 8Gb DIMMs, although I haven’t been able to verify this. Gigabyte’s documentation on similar motherboards is inconclusive as the earlier boards were from an time when 4Gb was all you could get. Again, I haven’t tried this but they are designed to handle 512Mb DIMMs. 1Gb and 4Gb certainly work and these tend to be available with any FS-12 you buy. At one time DDR2 ECC RAM was rather expensive. Not now. It’s much cheaper than DDR3 because, to be blunt, you can’t use it in very much these days.

And this is what makes the FS12 such a good buy: For about £150 you can get an eight-core processor with 64Gb of RAM. Bargain! And that’s before you look at the disk options.

The FS12, like most Dell Servers, is set up to run Windows and as a result requires a separate volume manager, on hardware designed to pretend Windows is looking at a disk. So-called “hardware” RAID. This takes the form of two PERC6/i cards occupying both PCIe cards on a riser. Fine if you want to run Windows or some other lightweight operating system, but PERC cards are about as naff as you can get for anything Unix-like. They work in RAID mode only, hiding the drives from the OS, and these are just a bit to old to be re-flashed in to anything useful.

The drives fit into a front-loading 12-way array with a SAS/SATA backplane. This is built in to the case; you can’t detach it and use it separately. Not without an angle grinder anyway, although if you really wanted to this would be a practical proposition. Note well that this is a backplane; not an expander, enclosure or anything so complex. Some Dell 2U servers like this do have an expander, which takes four SAS channels of SAS on a single cable and expands them to twelve, but this is the 1:1 version. And it’s an old one at that, using SFF-8484 connectors. If you’ve been using SAS for years you may still never have seen an SFF-8484 (AKA 32-pin Multi-lane). These didn’t last long and were quickly replaced with the far more sensible SFF-8487(AKA 36-pin Mini-SAS). However, if you can sort out the cables (as I will explain in a later post), this backplane has possibilities.

But as it stands you get a the PERCs and a 12-slot drive array that’s only good for Windows or Linux. Unless, that is, you remove the backplane and the PERCs and make use of the six 3Gb SATA sockets on the motherboard. You’ll have to leave the drives in place and connect the cables directly back, but how many drives do you need?

There is one unfortunate feature of these boxes that is hard to ignore: the cooling. It’s effective, but when you turn it on it sounds like a jet engine spooling up. And then it gets even louder. There a lot you can do about this and I’m experimenting with options, which I’ll explain in a later post, but in the mean time you need to give everyone ear defenders, or install it in an outbuilding and use a KVM extender. I’ve been knocking around data centres for over twenty years and I’ve never heard one this bad.

The cooling is actually accomplished by five fans. Two are 1U size in the PSU, and are probably as annoying as any other ~40mm fan. The real screamers are two 80mm and one 60mm fan positioned between the drive cage and the motherboard. A cowling directs the one 80mm fan across each CPU and its DIMMs and the 60mm gives airflow over the Northbridge and PCI slots. They all spin really fast – in excess of 10,000rpm, and although they have sense and control wires nothing seems to be adjusting them downwards to the required rate.

My suspicion is that either the customer didn’t care about noise but wanted to keep everything as cool as possible, or that whatever operating system was installed (ESX I suspect) had a custom daemon to control their speed via the SAS backplane. I shall be going in to cooling options later, but note that the motherboard has five monitored and software adjustable fan connectors that are currently not used.

So, in summary, you’re getting a lot for your money if its the kind of thing you want. It’s ideal as a high-performance Unix box with plenty of drive bays (preferably running BSD and ZFS). In this configuration it really shifts. Major bang-per-buck. Another idea I’ve had is using it for a flight simulator. That’s a lot of RAM and processors for the money. If you forego the SAS controllers in the PCIe slots and dump in a decent graphics card and sound board, it’s hard to see what’s could be better (and you get jet engine sound effects without a speaker).

So who should buy one of these? BSD geeks is the obvious answer. With a bit of tweaking they’re a dream. It can build-absolutely-everything in 20-30 minutes. For storage you can put fast SAS drives in and it goes like the wind, even at 3Gb bandwidth per drive. I don’t know if it works with FreeNAS but I can’t see why not – I’m using mostly FreeBSD 11.1 and the generic kernel is fine. And if you want to run a load of weird operating systems (like Windows XP) in VM format, it seems to work very well with the Xen hypervisor and Dom0 under FreeBSD. Or CentOS if you prefer.

So I shall end this review in true PCW style:

Pros:

Cheap
Lots of CPUs,
Lots of RAM
Lots of HD slots
Great for BSD/ZFS or VMs

Cons:

Noisy
no AES-NI
SAS needs upgrading
Limited PCI slots

As I’ve mentioned, the noise and SAS are easy and relatively cheap to fix, and thanks to BitCoin miners, even the PCI slot problem can be sorted. I’ll talk about this in a later post.