# Software SAS disk controller?



## Ignacio (Mar 19, 2021)

I just found some very cheap SAS (Serial Attached SCSI) disks for sale and wonder if there is a cheap way to use them with FreeBSD, I mean without having to buy a SAS controller, there are pin-to-pin adapters to convert them to SATA, but the controller needs to "speak" SAS anyway, maybe SAS can be software emulated somewhat?

These are the dmesg messages of my SATA controller:


```
kernel: ahci0: <Intel ICH8M+ (RAID) AHCI SATA controller> port 0xf0d0-0xf0d7,0xf0c0-0xf0c3,0xf0b0-0xf0b$
kernel: ahci0: attempting to allocate 1 MSI vectors (1 supported)
kernel: msi: routing MSI IRQ 269 to local APIC 4 vector 51
kernel: ahci0: using IRQ 269 for MSI                                                                    
kernel: ahci0: AHCI v1.30 with 6 6Gbps ports, Port Multiplier not supported
kernel: ahci0: Caps: 64bit NCQ SS ALP AL CLO 6Gbps PMD SSC PSC 32cmd EM eSATA 6ports
kernel: ahci0: Caps2: APST
```


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## SirDice (Mar 19, 2021)

SAS controllers generally are able to drive SATA and SAS drives. A SATA controller however cannot drive a SAS drive. This isn't software or driver related. Find a cheap (second hand) LSI controller that uses mpt(4), mps(4) or mfi(4), these are good solid cards and can handle both SAS and SATA disks.



Ignacio said:


> there are pin-to-pin adapters to convert them to SATA


SAS and SATA drives have the same connector.


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## Ignacio (Mar 28, 2021)

SirDice said:


> SAS and SATA drives have the same connector.



They don't, see attached image:





Anyway, thanks for the suggestions.


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## Snurg (Mar 28, 2021)

This is what I use:













SirDice said:


> SAS controllers generally are able to drive SATA and SAS drives. A SATA controller however cannot drive a SAS drive. This isn't software or driver related. Find a cheap (second hand) LSI controller that uses mpt(4), mps(4) or mfi(4), these are good solid cards and can handle both SAS and SATA disks.


This is what I did and what for I am using adapters like the one shown above.
Adapter was ~2 euros/pc, sent directly from PRC.

BTW, I read the MPT hostadapter can handle only up to 2TB drives?
Are the others better in this regard?


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## diizzy (Mar 28, 2021)

Anything that isn't ancient is fine, ie SAS2008 or newer if we're talking about LSI/Avago/Broadcom.
The "only" HBA's I know with issues are old Marvell based ones and LSI 1068E but those are well over 10y old by now.


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## sko (Mar 29, 2021)

SAS2008 based HBAs (e.g. the 9211-8i and all its OEM-variants) are dirt-cheap nowadays and SAS3008 HBAs are also available for <100$ if you are OK with used hardware. The chinese reference-design-clones are usually available at ~30-50$ for the SAS2008 and ~100-120$ for the SAS3008 and I even got a 9400 tri-mode HBA for 130EUR lately. These clones work perfectly fine - I've been using them in my personal systems and some non-critical systems at work for several years now and haven't had any problems with them.

I'd go for a proper SAS HBA over some adapters or other hacks any time, especially because you'd loose all benefits of SAS drives (i.e. more and deeper queues!) when using a 'dumb' SATA-controller.


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## 6502 (Mar 29, 2021)

I have also seen cheap SAS drives. I wonder whether their mechanics is better and more reliable than normal (green/blue) SATA drive (more metal instead of plastic for example)? Usually SAS drives are for servers running 24/7.


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## Ignacio (Mar 29, 2021)

sko said:


> I'd go for a proper SAS HBA over some adapters or other hacks any time, especially because you'd loose all benefits of SAS drives (i.e. more and deeper queues!) when using a 'dumb' SATA-controller.


Yes of course, but my main reason to look at SAS drives was reliability, I have the impression that actual SATA drives sold for domestic use (i.e. the typical Toshiba 2.5" sold by Amazon) are not as reliable as they were 5 or 10 years ago, I bought 2 and both developed a few unreadable sectors with less than 2000 hours, I noticed it because the whole disks are GELI encrypted, but if they weren't it would have gone unnoticed, there was no SMART error at all.


Snurg said:


> This is what I did and what for I am using adapters like the one shown above.
> Adapter was ~2 euros/pc, sent directly from PRC.


But those adapters are just pin-to-pin ones, they don't translate SAS te SATA, which controller you connect them to?


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## sko (Mar 29, 2021)

6502 said:


> more reliable than normal (green/blue) SATA drive



If you are referring to WD green and blue series, then any SAS drive is better than those. The green/blue series are consumer drives.
SAS drives are for server/workstation use and therefore intended for much higher workloads (i.e. 24/7). They have a much higher MTBF, longer warranty (usually 5 years) and much lower expected error rates (1 in 10^15 bits vs ~10^13 for consumer drives, if this is even specified). Also the support/RMA procedure is usually much quicker and less frustrating (enterprise support vs consumer support) - so no stupid questions asked about windows drivers/updates etc. and usually advanced RMA (i.e. you get a new drive delivered ASAP and return the defective one afterwards).

Another important thing to consider is the firmware of SAS drives, that is usually less problematic than for SATA drives when it comes to drive failures. I've seen several SATA drives that refused to just die and shut up but instead acted up in the most stupid and annoying ways - usually bringing the ZFS pool to a crawl and sometimes making it impossible to remove them from the pool. They also often even prevented the controller from POSTing, effectively blocking the reboot of the server and requiring remote-hands to get the system back online. (been there several times when we still had SATA drives in one of our remote servers)
SAS-drives usually just acknowledge they are dying and go dark (or at least report they are failing), so the system can continue working and a hot-spare can be activated immediately.


edit:
just to prevent any misunderstanding:
of course you shouldn't put any SAS drive in a desktop PC that gets rebooted (multiple times) every day. There are special workstation drives for this scenario, but server drives are intended to run 24/7. They can't handle thousands of on/off cycles and constant temperature changes as seen with normal desktop use!


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## ralphbsz (Mar 30, 2021)

6502 said:


> I have also seen cheap SAS drives. I wonder whether their mechanics is better and more reliable than normal (green/blue) SATA drive (more metal instead of plastic for example)? Usually SAS drives are for servers running 24/7.


It's more complicated than that.

About 15-20 years ago, what you said was correct: There were consumer disks (reasonable capacity, mediocre performance, very low cost), and enterprise disks (either very high capacity or very high performance, good reliability). Consumer disks had ATA interfaces (remember, the 40-pin ribbon cable), enterprise disks had SCS interfaces (50-pin ribbon cables). Matter-of-fact, Dave Anderson and Erik Riedel (both working at Seagate at the time) wrote a really nice summary paper with a title like "SCSI vs ATA: More than just an interface". In that they pointed out

Today, the situation is much more complex. A very large fraction of all 3.5" disks are enterprise disks, and over 90% of all those disks are sold to a very small number of customers (fundamentally the FAANG plus their Chinese counterparts). Consumers have mostly dropped out of the disk drive market. Enterprise disks come in a variety of grades, for different workloads, different applications, different reliability/performance/capacity expectations. Depending on the customer demands, most disk drive models are available in either SATA or SAS interfaces. Literally the same disk, same characteristics, just a different connector and firmware load. Some disk models are only available in SATA, because some of the large customers do not use SAS disks.

So what you say is partially true: there are better disks (but those are more expensive) and worse disks (cheaper). But this is not longer strongly correlated with SATA versus SAS.


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## Ignacio (Mar 30, 2021)

ralphbsz said:


> So what you say is partially true: there are better disks (but those are more expensive) and worse disks (cheaper). But this is not longer strongly correlated with SATA versus SAS.


So maybe you know where could I find some reliable SATA 2.5" disks? in Amazon and similar places just find bad ones,  I had specially bad experiences with some Toshibas made in Philippines.


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## 6502 (Mar 30, 2021)

I think this is the best 2.5" SATA:


			https://cpc.farnell.com/wd/wd10spsx/drive-black-2-5-sata-6gb-s-1tb/dp/CS33441#
		


It can be found at eBay as well - search for WD10SPSX.
​


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## diizzy (Mar 30, 2021)

Just get a SSD that isn't dirt cheap?


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## Phishfry (Mar 30, 2021)

Ignacio said:


> Intel ICH8M+ (RAID) AHCI SATA controller


You need to step it up a decade to PCIe 3.0 bus.
That is some rather dated hardware. How much longer are you expecting that to live? Circa 2006.
Maybe you should consider an updated motherboard first. Then shop for a nice NVMe.


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## ralphbsz (Mar 30, 2021)

2.5" disks are a particularly strange breed. There are super fast ones (10K or even 15K RPM), with SAS interfaces, for enterprise use. Often very small capacity (less than 1TB), but really good speed (latency is obvious, and IOps is also fabulous, albeit with high power consumption). There are cheap ones, made for laptops, with SATA interface. Typically very low RPM (5400 or so), typically good capacity. They tend to be built to survive mechanical shock, but life in a laptop is just really hard for a disk (temperature, vibration, shock). 

Both kinds are dying out. The high-speed ones because SSDs have eaten their lunch. The laptop ones because most laptops sold today come with SSD. I think the best and last of that generation were the IBM/Hitachi Travelstar disks; I don't know whether WD ever built a worthy successor under their own brand name. My suggestion: If this is a laptop, buy a SSD in the same for factor. I'm pretty fond of the Crucial SSDs for consumers, inexpensive and decent quality. If this is a desktop machine, either go to a 3.5" disk (much more selection), or again use an SSD, or follow Phishfry's advice and go to NVMe.

And note that "bad experience with ..." does not generalize. All disk vendors occasionally have lemons. This does not mean that all drives in made in the Philippines or made by Toshiba are junk.


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