Supermicro 3u 16bay 3.5" chassis with SAS2 expander

Mark

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Nov 6, 2014
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also note that the sas2 is 6.0/gb (sata II) which is a great backplane, but the included raid card (5805) is only 3.0/gb (not sata II). Im not sure how you plan on interfacing with the backplane, but if your going to use the 5805, i just detailed a huge amount of issues i had with getting any type of sata drive beyond 8x drives to spin up on an adaptec 5805 (and i also tried a 5405z) with a BPN-SAS-846EL1 (not the sas2, this one is the 1.5/gb version) in this thread:

STH forum link
Locked in a deal with the seller for 300+shipping for:
Chassis: SC846E16-R1200B with 24 3.5in drive trays
Power Supply: 2 x PWS-1K21P-1R
Power Distributor: PDB-PT846-8824
Backplane: BPN-SAS2-846EL1
Mounting Rails: MCP-290-00057-0N

I have a X9DR7-LN4F with an LSI2308 that I will be using to interface with the back plane. I think I did well. Can't wait for it to arrive.
 

canta

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If you don't mind the extra 1U it almost seems like a better deal then the original one on this thread. I'm a little salty.
this is up to your needs.
on mine:
I have 2 4U 24 bays (AIC and Supermicro) servers, since due on downsizing HDs to reduce power consumption and moving bigger 2T and 3T (ehemm just for me 3T is already big, hopefully 4g-6G would drop dramtically within 3 years).
I dumps all (ehem) 500G and 1T HDs to 24 bays servers as secondary backups on lack-rack.
and
moves to 2T/3T with additional new drives to two 3U (this thread)servers. power consumption on HDs reduces a lot from 16HDs to 8HDs/server with more space on rack for my router/baremetal/misc items.

whatever something works on you, sticks on that.
 
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eduncan911

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This is a great thread and clarified a few things I've suspected about these 3U and 4U systems. I wanted to chime in (and subscribe!) with some additional facts I've read (and partially experienced).

Let me discuss the Supermicro 24-bay chassises, specifically the SC846E1 variant. (E16 variant already has the SAS2 backplane, so if you can get one of the E16 models cheap - DO IT!).

SAS - > SAS2

The SAS1 backplane on the older Supermicro SC846E1 models (part number SAS-846EL) can support up to 4TB (maybe 6TB), but only up to 4 drives total. Once you exceed 4 drives though, anything larger than 2TB drives are not recognized. I suspect this is because of the single-port expander, which a single port is actually 4 SAS/SATA ports in that single cable and the expander just does a straight pass through - then it's up to your IBM/LSI/Adaptec controller to support the large drives. But once you install more than 4 drives, the Expander in the backplane takes over, and the SAS (non-SAS2) firmware doesn't support anything larger than 2TB.

^- per Supermicro tech support and other accounts I've read only.

You want the SAS2 backplanes, Supermicro part number SAS2-846EL to be exact for the 24-bay SC846E1 chassis. Be careful when looking at any 24-bay Supermicro chassis though. "E16" means SAS2, "E1" is SAS1.

The SAS2 backplanes support 4TB (and maybe larger) drives, in expanded mode. They also support higher bandwidth (6Gbps/550 MB/s) per port as well, for you SSD guys.

There may be a little concern about these drive Expanders with 16 to 24 drives loaded up... On a single 4-port SFF-8087 cable with a SAS2 Backplane, that's a max bandwidth of 24Gbps, or about 2200 MB/s, which is pretty damn fast for our little home server needs. The SAS1 in contrast is only 1100 MB/s max bandwidth.

This is a different story with "L2" backplane modes (see below).

Supermicro SC846E1 vs SC846E16 variants

In short, the "E1" is the SAS1 3 Gbps version, and the "E16" is the newer SAS2 6 Gbps version.

But, you can pick up the older E1 versions and upgrade the backplane usually pretty cheap if you want for a deal on the SAS2 part number I posted above.

SAS2-846EL1 vs SAS2-846EL2

Note the "L1" vs "L2". It was already mentioned in this thread that some backplanes have two Expanders instead of one Expander chips. That is correct, and you can look for the "L1" and "L2" designation on the backplane to know.

L1 = One Expander chip
L2 = Two Expander chips

They offer these two-chip solutions for one main reason (also already mentioned in this thread):

* Redundancy in case the first Expander fails, the 2nd one automatically takes over. This is in the operating manuals for the backplanes.

Now, there is some very limited information in that it does bandwidth splitting across the L2 systems. I haven't gotten clarification for that; but again, we don't need more thatn 2.2 TB/s for our home servers (which the SAS2 L1 units are).

Spindown w/IBM M1015 - passthrough, no Expanders

Spindown... In my original WHS I built in 2008, I had all 10 drives spinning down. Since I moved to my IBM M1015s, flashed to LSI firmware, I haven't noticed any drives spinning down. I am still running a few 7 year old 1 TB HDDs, spinning at all times for a few years now.

Has anyone been able to get their drives to spin down? The StableBit DrivePool software I use says they can issue the command; but, it can be ignored by the controllers.

While everything seems fine, and I don't miss the "5-8 second delay" I used to have for drives spinning up, the amount of heat generated in my current 14-drive system is a lot more than I would like (not to mention the power consumption).

IBM M1015 - 2x SFF-8087 "Firmware" / Flash / IT Mode

These are the super-cheap LSI 6Gbps SATA3 controller cards that were mentioned in this thread. I picked up two for $90 total on eBay almost 2 years ago, flashed them to the LSI firmware, and have been enjoying up to 500MB/s from my SSDs connected to them.

http://www.servethehome.com/ibm-m1015-part-1-started-lsi-92208i/

^- that's the great article that explains everything.

Most of these Supermicro chassis though already include a card. But...

The SFF-8087 Controller Card Included in SAS1 chassis

Be careful when getting an older chassis that you plan on upgrading the backplane (see below for backplane upgrades). If it is a non-SAS2 chassis (just SAS), then most likely the controller card that comes with it is only 3Gbps (280 MB/s) per port. Some you can flash to get 4 TB drives recognized, but see previous notes about the SAS1 expander firmware that does not.

What I've seen in Supermicro's tech specs, and all the units on eBay for sale (I've been searching for months) is that if it has a SAS2 backplane, then it has a 6 Gbps controller.

Otherwise, plan on getting one of the IBM M1015s mentioned above, flash it to the LSI IT mode, and be done.

SAS2, on the cheap (as of July 2015)

Me? I've found out that you can upgrade the older chassis to use the newer SAS2 backplanes (though it voids Supermicro's warranty). Let's look at how what this would cost:

* Supermicro Superchassis SC846E1 24-bay SAS1 chassis: $150-$250 on eBay
* Supermicro SAS2-846EL1 Backplane: $150

Looking to be $300 to $400. Most of the time I've seen these for around $250 for the chassis and $300 for the backplane, which is $500+. But setup a price alert and sometimes those chassis come in cheaper as well as the SAS2 backplanes (I got mine for $150 shipped).

The original deal in this thread is awesome - a 16bay, fully functional server with SAS2 and quiet 1200W PSUs. I've been waiting since April for more to pop up, but they haven't. Boo.

I am currently in talks with some local vendors about sourcing an older SC846E1 with a failing backplane (cause I already have the SAS2 backplane to replace it) and no PSUs (so I can use my own).

Replace the PSUs, with any ATX or even the 900W Platinum

Oh, that's another note... You can just drop the PSUs and housing all together and a standard ATX will fit in nice.

Are You Looking For A Less Expensive Norco 4220 / 4224 Alternative? - AVS Forum | Home Theater Discussions And Reviews



In addition, you don't have to go out looking for the 1200W PSUs - some won't even fit. See this reddit thread for good details about replacing them with 900W Platinum units which are very quiet:

Supermicro PWS-920P-1R

Replacement Power Supplies for Supermicro SC846E1-R900B Chassis : homelab


Plex Media Server (PMS)

Those of you that plan on running Plex (and you really should try it) may be very interested in these cheap LGA1366 Xeon mobos/cpus that come in these 3U 16 bay and 4U 24 bay older servers. Most of the cheap $90 quad core Xeon CPUs you'll find in these auctions for another $100 actually have a CPU PassMark of over 7000 or even 8000. That's on par with an Intel 980X Hex core. What does the CPU PassMark mean? It means more concurrent multiple streams. I've been running into this issue since I setup my extended family on my Plex server. I've seen up to 9 streams at once.

What I am getting at is don't dump those cheap Xeons if you do pick up one of the complete systems.

Ok, that's my first post here...
 
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whitey

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Good show sir for a first post, filled w/ knowledge and good tips/tricks/lessons-learned!
 

PigLover

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@eduncan911 - great post. Lots of simple truth in there, stated clearly.

A couple of comments:

On upgrading the backplane: very true. The backplanes are reasonably interchangeable and it is pretty simple surgery. However, if you haven't bought your chassis yet you generally get a better overall deal on eBay just buying one with the SAS2 backplane from the get-go. Just make sure you message the seller an confirm what you are getting.

On the SC836 chassis in general: great chassis. Have one running. But in hindsight, I'd suggest that you get a better deal with the 4u SC846 (4u 24x 3.5"). Unless that 1U of space is a deal breaker, of course. The 846 is more common on eBay and generally sells at the same or lower cost than the 836. Do your shopping before you buy.
 

eduncan911

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Oh, maybe I wasn't clear... I was only talking about the SC846. :) I'll edit the post now.

The "E16" variant is the one with the SAS2 backplane, and are usually north of $500 or more.

The "E1" variant, specifically the SC846E1, is the one with the older SAS1 backplane that can be interchanged with the part number I posted earlier. These can be had for as little as $180, plus some hefty shipping fees.
 

james23

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SAS - > SAS2

The SAS1 backplane on the older Supermicro SC846E1 models (part number SAS-846EL) can support up to 4TB (maybe 6TB), but only up to 4 drives total. Once you exceed 4 drives though, anything larger than 2TB drives are not recognized. I suspect this is because of the single-port expander, which a single port is actually 4 SAS/SATA ports in that single cable and the expander just does a straight pass through - then it's up to your IBM/LSI/Adaptec controller to support the large drives. But once you install more than 4 drives, the Expander in the backplane takes over, and the SAS (non-SAS2) firmware doesn't support anything larger than 2TB pick up one of the complete systems.

Wow! Is this true?? That's the first I've ever heard of the SAS1 el1 expander) only supporting drives up to 2 TB drives MAX) not supporting more than four drive simultaneously , If those drives are over 2tb?

This may explain The issues I was having in another thread I posted about major problems with my Adaptic 5805 recognizing 12x 3tb HUA drives on this backplane (it would randomly only spent up eight, randomly eight of the 12 drives at start up causing the array to break during my testing Phase)

Can someone confirm this? Supermicro tech has been known to make contradicting statements if the only source for this is A SM tech

Tks
 

eduncan911

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Wow! Is this true?? That's the first I've ever heard of the SAS1 el1 expander) only supporting drives up to 2 TB drives MAX) not supporting more than four drive simultaneously , If those drives are over 2tb?
Slight correction to that question... It will support as many drives as the Expander is touching (24?) and even write to them. But, once you exceed 4 (maybe 8) drives, the largest the SAS1 version of the Expander will support is 2 TB. I say "4" as that is what most have report - some, like yourself, have said 8 drives spin up sometimes. But it won't be more drives than that with the SAS1 Expander backplanes and 3TB or larger HDDs.

Remember, I am talking about the Supermicro 2U, 3U and 4U backplane units that have the Expander here. For example, the 24-bay SAS1 backplane is part number SAS-846EL1 or SAS-846EL2 - avoid these. You want the Supermicro backplane SAS2-846EL1 or SAS2-846EL2 (note the "2" in the "SAS2" part) in the 24bay chassis you are looking at.

This is why you should get the SAS2 backplanes. Not only do they go to 4TB and beyond, but they also support SSDs (I haven't looked it up, but one IT guy told me they support TRIM on SAS2 as well).

What I was mentioning above is that you can find deals on these SAS2-846EL SAS2 backplane expanders on eBay. I got mine for $150 shipped (there was 3 over the weekend, all 3 sold).

--

Remember, the only reason to get a backplane with an SAS2 Expander is if you don't have any HBA cards and need to buy them. Getting a chassis with an Expander built-in saves cost in the total build - as you don't need to buy 1x HBA 4-port SFF-8087 card + 24+ Expander card, or the direct route with 3x 8-port HBAs. Either setup will run close to $300 to $370 once you add in those break-out cables.

Well, another reason is tidy... Instead of 24 SATA cables snaking everywhere unwildy, you just have a single SFF-8087 cable. :)

Well, some would argue that they would want the SATAs directly connected to each port - no expander. I personally subscribed to this club (e.g. I want the option to do RAID) and got my two IBM M1015s that I flashed to the LSI firmware, ready for this day. That's 2x8 ports per card, 16 total.

But now that I am getting ready for my budget server build, I'm finding the $460 cost of an "empty" NORCO quite expensive when I can get a Supermicro SC846E1 (the "E1" means "Has Expander Chip") all ready to go for $180 (SAS1 only though). Therefore, I found the SAS2 backplane for $150 and BAM - that's just $330 compared to the $460 NORCO, in a chassis that supports EE-ATX mobos (and beter build quality?).

Also, thanks to this thread, I now see the LSI Expander chips in these Supermicro chassis properly registers what HDD by blinking its LED - so if one fails, you can quickly find it. That's what sold me so I don't have to track my serial numbers and HBA assignments any longer! No more of this needed!

Setup
---------
ich00:hda00 - MyDigitalSSD 128GB SSD : C:\ (HITOSHI, Windows Server 2012 os)
ich00:hda01 - OCZ Vertex3 240GB SSD : D:\hyper-v (KIRK, SPOCK, ALICE, LICENSING)
ich00:hda02 - WD Green 500GB : E:\nzb (search/scratch/staging drive)
ich00:hda03 - EMPTY
ich00:hda04 - EMPTY
ich00:hda05 - EMPTY

DrivePool Assignment - A:

hba01:port00:hda00 - K: Seagate NAS 4TB (pool)
hba01:port00:hda01 - L: Seagate NAS 4TB (pool)
hba01:port00:hda02 - M: WD Green 2TB (pool)
hba01:port00:hda03 - N: WD Green 1TB (pool)
hba01:port01:hda04 - O: Seagate NAS 4TB (pool)
hba01:port01:hda05 - P: Seagate NAS 4TB (pool)
hba01:port01:hda06 - Q: RESERVED
hba01:port01:hda07 - R: RESERVED

hba02:port00:hda00 - S: Seagate NAS 4TB (pool)
hba02:port00:hda01 - T: Seagate NAS 4TB (pool)
hba02:port00:hda02 - U: WD Green 1.5TB (pool)
hba02:port00:hda03 - V: WD Green 1TB (pool)
hba02:port01:hda04 - W: Seagate NAS 4TB (pool)
hba02:port01:hda05 - X: Seagate NAS 4TB (pool)
hba02:port01:hda06 - Y: RESERVED
hba02:port01:hda07 - Z: RESERVED

NOTE: For serial numbers, I am fortunate enough that StableBit's DrivePool/Scanner exposes what serial number each drive has. So if one fails, or starts to fail, I can take that serial number and lookup what drive letter it is assigned to. Then I take that drive letter and match it to above, to know exactly where it is in my Antec Twelve Hundred (which was a gift).

^- I'll loose that ability, I think, when moving to an Expander chip/card. I don't know if it passes that information back to the HBA or not. Worse case, I can use LSI's management software to flash the drive that failed (according to this thread). That works for me for an expander!

Makes me wonder what I'll do with with the other SFF-8087 port on my IBM M1015... Even more so, what am I going to do with my 2nd IBM M1015 just sitting there? lol

I read the manuals for the Supermicro 24bay chassis w/backplanes and they only use a single SFF-8087 connector (2x connectors on the failover backplanes). Wondering what will happen if I connect both SFF-8087s to the backplane, even though it says the 2nd and 3rd connectors are for daisy chaining to additional backplanes.
 
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canta

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Slight correction to that question... It will support as many drives as the Expander is touching (24?) and even write to them. But, once you exceed 4 (maybe 8) drives, the largest the SAS1 version of the Expander will support is 2 TB. I say "4" as that is what most have report - some, like yourself, have said 8 drives spin up sometimes. But it won't be more drives than that with the SAS1 Expander backplanes and 3TB or larger HDDs.

Remember, I am talking about the Supermicro 2U, 3U and 4U backplane units that have the Expander here. For example, the 24-bay SAS1 backplane is part number SAS-846EL1 or SAS-846EL2 - avoid these. You want the Supermicro backplane SAS2-846EL1 or SAS2-846EL2 (note the "2" in the "SAS2" part) in the 24bay chassis you are looking at.

This is why you should get the SAS2 backplanes. Not only do they go to 4TB and beyond, but they also support SSDs (I haven't looked it up, but one IT guy told me they support TRIM on SAS2 as well).

What I was mentioning above is that you can find deals on these SAS2-846EL SAS2 backplane expanders on eBay. I got mine for $150 shipped (there was 3 over the weekend, all 3 sold).
...................
well, SAS1 expander is a nightmare when using 2TB or greater 0n my understanding..
I still keep Chenbro SAS1 Expander that remind me the past nightmare,
4 drives was OK, more than that caused random failed HD discovery. I believe due on timeout during discovery..
yes.. 3T is supported too. this is the matter discovery time-out...

I think TRIM (SATA only) is provided as is in SATA tunneling . SAS uses SCSI UNMAP.

this was depend on the SAS1 implementation on vendor to support TRIM or not
SAS2 already adopted TRIM (SATA)....

I just check on ebay, SAS2 846 (has all PWM fans that is very helpful than old mode non-PWM, buying SM PWM fans are $$ that add cost much in total) with 1200W platinum has gone dried...
I saw some this week and already gone.
the price should be 400-500 with best offer.. + shipping.
I got one for less $400 including shipping early this year and still sitting on the floor... just random act that trigger by this forum hahaha. I did best-offer and got accepted,

I already has 1x846 sas2 expander version(all PWM fans) with platinum PSU, 1x846 SATA version(old model with non PWM-fans) - modded with desktop fans and PSU, 2X 836 sas2 expander(all PWM fans) with 500W platinum PSU, 1x826 sata version (all PWM fans) with 500W platinum PSU, and last on least Heavily modded AIC.

I took out everything from AIC due on power issue on backplane... one raw on backplane causes HD headaches when installed..
tried to revive this AIC before jumping on 836 and failed to make it worked...:(.
need backplane replacement on my understanding..

and no more case for me
 
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eduncan911

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I just check on ebay, SAS2 846 (has all PWM fans that is very helpful than old mode non-PWM, buying SM PWM fans are $$ that add cost much in total) with 1200W platinum has gone dried...
I saw some this week and already gone.
the price should be 400-500 with best offer.. + shipping.
I got one for less $400 including shipping early this year and still sitting on the floor... just random act that trigger by this forum hahaha. I did best-offer and got accepted,
You just need to setup a PriceAlert on one of these 3rd party sites to be alerted when an exact part number is posted. That's how I got my SAS2-846EL1 backplane for $150 shipped. Check.

Today, I have several offers for a Supermicro SC846E1 Chassis, minus the Backplane and minus the PSUs for $100 to $120, plus about $50 shipping. Figured if these PSUs are not efficient, too loud and replacable, why should I pay for them and why to pay for shipping? :) It worked! Several of these eBay vendors will strip these chassis bare.

So that's a chassis for $170, backplane for $150 for $320 total shipped. I have several Gold and Platinum ATX PSUs already so I don't mind just slapping on of them in.

I already has 1x846 sas2 expander version(all PWM fans) with platinum PSU, 1x846 SATA version(old model with non PWM-fans) - modded with desktop fans and PSU, 2X 836 sas2 expander(all PWM fans) with 500W platinum PSU, 1x826 sata version (all PWM fans) with 500W platinum PSU, and last on least Heavily modded AIC.
That's a nice collection there. I think some forum members here might want to hit you up for some of these. :)

I too have several PWM fans as I highly prefer them over 3-pin (I've built my own PWM controllers before).[/QUOTE]
 

canta

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I have several Gold and Platinum ATX PSUs already so I don't mind just slapping on of them in.
.....


......:)

I too have several PWM fans as I highly prefer them over 3-pin (I've built my own PWM controllers before).
[/QUOTE]
I prefer SM platinum PSU :D as today. 501P 0r 920SQ

build your own PWM controller is just a hack :p. it worked but not optimal and making "Grinding" sound on low rpm. and consume more power. as I know server grade 2 ball bearing fan non-pwm with 40mm-50mm thicknes minimally 1-2A range :D.
the spec 4 PIN PWM is pretty common and can be look into. 20Khz-30Khz, ideally 25Khz with some mumbo jumbo low and high duration delta time.:D

on real server grade PWM fan, you can lower down very low rpm without weird noise.

if you see on my other thread, I build (on progress) controller of closed rack server wuth 6 PWM fan deltas 120mm dynamically .
That was tedious since I had to look on delta fan specs and rpm sloop before implementing in the code.
delta and nidec fan spec is 20Khz minimally - 50Khz maximally :D..
I would stop on mumbo jumbo PWM fans :D...

I love two ball bearing PWM fan especially delta, sunon maglev(hard to find cheap), and nidec(hard to find cheap!).
 

eduncan911

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Yeah, I just found this thread... https://forums.servethehome.com/ind...ro-4u-24-bay-chassis-with-sas2-expander.4485/

I didn't realize the older SAS1 versions don't have PWM fan headers on the SAS1 backplane. Makes me wonder if the chassis itself has PWM fans, just no PWM fan headers. Humm...

And also within that thread is the IPMI screenshots showing power consumption. Dang, those are nice with the SM PSUs...

I have a few vendors with the Gold 1200 versions of the PSUs that he'll include for $45 each. On the fience about the Gold versions as people hate the non-Gold/non-Platinums, but love the Platinums. Not sure on Golds yet...
 

eduncan911

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Man, just when I get ready to buy I find more and more threads about the SC846...

Looking to voice my current delima, and others to chime in...

Ok, here's my goals:

* Something light-ish (I can remove the drives from the SC846, I'm getting old)
* 16+ drives
* 6Gbps+
* Quiet-ish (Gold 1200W sounds too loud from what others describe)

Ok, here's what I got:

* Supermicro SAS2EL1 backplane
* 2x IBM M1015s flashed to IT mode (currently driving 14 6Gbps HDDs)
* Core i7 950, mobo, 12GB ram

Notice I did not say I had a PSU. I do have a spare platinum ATX 1200W single-rail PSU, but prefer not to use it.

Here's the deals I'm currently debating:

Option 1) 24-bay monster
SC846E1 chassis, minus backplane and minus PSUs for $120 ($170 shipped) are the deals I have on deck. I've asked several sellers and they are willing to strip it down since I already have the SAS2 backplane.

Do the SC846E1 "SAS1" chassis come with PWM fans? Or only 3-pin fans? I know the SAS1 backplane has just 3pin fan headers. I am asking about the actual fans in the chassis. I highly prefer PWM as that's how I control it for other systems.

This is ~$320 total shipped for a SC846E1 w/SAS2 backplane I will install.

-"Quiet" PSUs

Nothing to sale to recoup costs.

Option 2) Supermicro 3U 16bay w/SAS2, 2x900W & X8-series mobo + Xeon
My concern here is the noise of the PSUs, and power draw of older Xeons...

On eBay for $300 + $80 shipping, that's $380. But it's a complete system.

-"Quiet" PSUs

Uses more power at idle.

+ Sell my SAS2 backplane. $150 or so profit
+ Sell my Core i7 950 + mobo + ram. $250 or so profit.


Humm, now that I type this out... It's a no-brainer I guess.

Am I crazy for thinking of bailing on the 4U 24bay chassis/setup for a 3U?
 

canta

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.....

Here's the deals I'm currently debating:

Option 1) 24-bay monster
SC846E1 chassis, minus backplane and minus PSUs for $120 ($170 shipped) are the deals I have on deck. I've asked several sellers and they are willing to strip it down since I already have the SAS2 backplane.

Do the SC846E1 "SAS1" chassis come with PWM fans? Or only 3-pin fans? I know the SAS1 backplane has just 3pin fan headers. I am asking about the actual fans in the chassis. I highly prefer PWM as that's how I control it for other systems.

This is ~$320 total shipped for a SC846E1 w/SAS2 backplane I will install.

-"Quiet" PSUs

Nothing to sale to recoup costs.

Option 2) Supermicro 3U 16bay w/SAS2, 2x900W & X8-series mobo + Xeon
My concern here is the noise of the PSUs, and power draw of older Xeons...

On eBay for $300 + $80 shipping, that's $380. But it's a complete system.

-"Quiet" PSUs

Uses more power at idle.

+ Sell my SAS2 backplane. $150 or so profit
+ Sell my Core i7 950 + mobo + ram. $250 or so profit.


Humm, now that I type this out... It's a no-brainer I guess.

Am I crazy for thinking of bailing on the 4U 24bay chassis/setup for a 3U?
if you already collecting 846 parts, go for it. just a friendly reminder, this seems your 846 case is old model and only has non-pwm fan (except two slims of 80mm on the exhaust that has pwm).
you can build pwm modules as you mentioned for each fan for non PWM fans with some passive components and a transistor/mosfet. Mosfet is overkilled on my understanding. just one reminder: this trial and error by testing non-pwm fans can works OK with this hack, such as: no loud grinding/whining noise.

I prefer 3U starting on two years ago due on 3T or greater size is common...
less space less weight..
This was the reason, I picked 2X 3U sas2 expander SM case with platinum PSU. Yes... my requirement was all fans must be PWMed, since buying seperate SM PWM fans is much $$ (even on used one!!)

3U can be installed with 16 drives or 14 drives for data and 2 drives for OS in raid1 configuration.
if you install 14X3T with raid6/raidz2/raidz3. there is a big fat space, or install 4T or 5T...

if you go to 3U option, MAKE sure to ask Seller that they sell indeed all PWM fans (4 cables) deal.
SM PSU is not hard to find cheap for gold or 1200W platinum (prefer this than gold).
1200W platinum is not very loud compared with old one or gold version and can be bought @$40-50 with free shipping..
honestly I went from 1200W to 500W platinum and save 20W.
IPMI is very helpful and you can monitor power consumption with SM PSU as long as you installed workstation or server motherboard that supported.

Honestly, I always buy empty case and deal with seller to strip down "old" motherboard and negotiate to add platiunum psu if they have it.

good luck and have fun!