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Some insights into SLOG/ZIL with ZFS on FreeNAS

jgreco

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That seems like a very bad idea.
I actually wondered if that was possible a long time ago. Then I had better things to do with my hours. I'd actually bet that it is possible if you try hard enough, but the question is "how hard is that."

No, it's not a typo. The SAS2208 is on the IBM MegaRaid M5110 card that came with the server. It is set to JBOD mode. FreeNAS defaults to using mrsas driver (rather than the older mfi), passes all info to camcontrol. The drives show up as da12 (Sandisk SSD Plus boot drive), da13 and da14 (the S3700s). smartctl works properly on all drives I plugged in so far (thee types of SSDs). Are there any known issues with this configuration?
Well the basic issue is that there are about zero hours of mileage.

One of the reasons we promote crossflashing to IT mode is because there's probably in excess of a billion driver-hours on the LSI HBA IT stuff. ZFS pushes I/O systems hard and it isn't really good enough to have 99.8% or 99.9% or 99.999% "correctness". We know the LSI HBA's in IT with the proper firmware/driver work correctly under adverse conditions, under normal conditions, etc.

The PC enthusiast who is used to overclocking and getting the occasional BSOD, that mindset isn't particularly good with respect to server builds. We assume that you're building FreeNAS to provide a safe haven for your valuable data. Using untested and unproven hardware is fundamentally risky, and putting thousands of hours of runtime on it just to pass basic testing is something most enthusiasts are not willing to do.

The MFI driver is known (firsthand, by me) to be good - not great, but good - but more than a little quirky. I suppose the MRSAS driver could be better. I'd actually love for it to be better. It'd be great if that were the case because so many systems come with LSI RAID controllers.

It's an option, although I'm a bit worried that IBM server will complain if I put a different card in the storage slot (like Dell servers do). And M5110 is free :)
 

2nd-in-charge

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2nd-in-charge

FreeNAS Aware
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Jan 10, 2017
Messages
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Thanks
18
I replaced the M5110 with M1215, cross-flashed it to 9300-8i IT firmware. MPR driver gets invoked:
Code:
root@pm2[~]# dmesg | grep mpr0
mpr0: <Avago Technologies (LSI) SAS3008> port 0x2000-0x20ff mem 0xa9b40000-0xa9b4ffff,0xa9b00000-0xa9b3ffff irq 42 at device 0.0 numa-domain 0 on pci4
mpr0: Firmware: 16.00.01.00, Driver: 18.03.00.00-fbsd
...
da12 at mpr0 bus 0 scbus1 target 4 lun 0
da14 at mpr0 bus 0 scbus1 target 6 lun 0
da13 at mpr0 bus 0 scbus1 target 5 lun 0

The drives were detected (da12 as boot mirror, da13/da14 as a mirrored slog).
Smart works as well.
However after I removed the log from the pool (and rebooted a few times), I still cannot run slog benchmark
Edit: ahh, found the reason for "operation not permitted". The drives were still used for swap. The latency of SAS3008 is pretty bad. Will post the result in the slog testing thread.

Is mpr the right diver and is it also "low mileage"?
 
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