Suggested Rig, please
 

I'm thinking of buying a new rig for factorising big numbers using yafu. Obviously I'd like it to have several cores, to make it run reasonably fast, but I don't want to spend too many quid on something that may well be over the top.

Can anyone make any decent suggestions?

How often are you going to be doing the work and how comfortable are you with linux? You might be better off renting cloud services. You could engage a large amount of compute for a short time, finish the job and not have to keep paying off the machine.

[QUOTE=Uncwilly;581899]You might be better off renting cloud services.[/QUOTE]

Seconded. Just be sure to configure persistent storage, and then use GCE's "Preemptable" and/or AWS's "Spot" instances, and you'll definitely get more "bang for the buck"!

If you haven't already, sign up for Google's free $300 credit trial to get a feel for the environment. AWS's free trial doesn't give you anything worth computing on. Oh, and of course Azure; its free trial is also worth experimenting with, but I've found their compute is the most expensive of all the options.

If you do prefer physically-owned hardware, I suggest used Xeon workstations, such as HP Z640 or Z840. Something around $1000 should get you twin 10- or 12-core Haswell Xeons and 64GB memory.

Then again, I'm not sure that's faster than a new/current 16-core AMD Ryzen, which is what I would likely choose if I were building my own machine from new parts.

For GNFS jobs, CADO on linux is much faster than Yafu/GGNFS; we haven't collected enough data yet on SNFS jobs to compare the two packages.

Physically for bang-for-buck IMO it's either go cheap with a 6 core Zen2/3, or go bold with a second hand server (but that's rough in the UK with our electricity prices, if better-electrically-blessed people are suggesting cloud then that's saying something).

Depending on how comfortable you are with dirtying your hands with strange hardware, and in tone with what Curtis said, try googling your favorite rubbish-selling site (like ebay, amazon, aliexpress, etc) for "lga2011 set". With a bit of luck, some average risk, and lots of work (work includes searching) you can get an 80-to-240-cores machine for as much as 2000-to-4000-bucks (which includes 5-to-10-sets, the power supplies you will have to add separate, local buy, a net switch, a monitor, etc.).

We posted about that in [URL="https://www.mersenneforum.org/showthread.php?p=575626"]Mike's yolo thread[/URL] some time ago.

Edit: if you buy from Amazon, maybe you also consider [URL="https://www.mersenneforum.org/showthread.php?p=573636"]this[/URL].

[QUOTE=BudgieJane;581895]I'm thinking of buying a new rig for factorising big numbers using yafu. Obviously I'd like it to have several cores, to make it run reasonably fast, but I don't want to spend too many quid on something that may well be over the top.

Can anyone make any decent suggestions?[/QUOTE]

Maybe i can show you my rig here i just built.

It is 2 x 22 core Xeon e5-2699 v4 ES processors.
So ES means: engineering sample.
that means: not supported officially - but they work ok
in china it seems they produced at least a 100k+ of them, so probably for an old supercomputer they were used.

They go for 389 dollar each - when i bought 2 of them a few months ago.

You will need a good motherboard for it and psu.
I bought a supermicro XDAI motherboard for it. This motherboard is not overly expensive.

It eats 360 watt under full load - yet the cpu's are close to each other so under full load you can only use watercooling practical.

I can show some photos.

I'm not having it in a rackmount case as that is too noisy so it is a 100% custom build.

The watercooling i built is custom - not recommended to do unless you know what you are doing.
I bought 2 radiators which can mount 12 cm fans and put 2 noctua fans on each radiator.

some 3d printed plastic holds the gpu - as i need a reasonably fast gpu for it - the box main purpose is a CAD computer to me. Simply the rmaining system time is for prime numbers and sometimes my chessprogram Diep :)

Now i already had a psu. Under full load 360 watt and add the gpu. The gpu i have is idle 22 watt yet in theory could eat 250+ watt under full load. It is very old AMD one that can do a high resolution and is delivering some Tflops single precision though it would be 0.5 Tflops double precision - for graphics only single precision matters obviously and a resolution of 3840x1200 for the CAD spreaded over 2 TFTs.

You can get away with a lightweight gpu there for 25 euro newprice - or a second hand one.

Now the better psu's you want to give just over 50% load. So you will want for a rig like this at least a 700 watt psu preferably of course 80+.

Those are not so extremely cheap. Preferably you get a psu that is modular so that you can have enough cables for the motherboard. It needs 24 pins + 2x 8 pins for this motherboard.

then the RAM i use cheap ram from china 8 sticks. killsre or something. ddr4 ecc reg.
not sure of current price.

the waterblocks i use cheap gpu waterblocks and some ABS 3d printed stuff moving over it and with simple m4 bolts (din912) from which i have thousands in stock of course as i design 3d printers and robotics, i bolt it.

So all together if you would build this new and buy everything as i reused PSU and harddrives and bunch of fans it's like 1500-1700 euro depending upon where you live. Cheaper in USA.

Ah photo of my rig exceeds the 1MB max size. it's 1.48MB. Doh. And this is linux this box - no good editor. Will do under windows soon in simple paint.exe resize it to smaller.

p.s. for ES processors cheap chinese X99 motherboards will not work.