Mirror SATA DOM's

[diedrichg]

Few SSDs these days are SLC.

You are correct, I misspoke and I wrote that way too early this morning.

 

[STREBLO]

With the mirroring is it basically duplicating everything it writes and writing it on to both discs? Then if there's a failure it tries to reboot and if you have your boot preferences right it should in theory boot on to the other device ? If it doesn't boot automatically, you should be able to reboot by hand and boot on to the second device no problem right?

Is there somewhere that has some in-depth information on how mirrored boot devices work? I couldn't find anything in the FreeNAS guide.

 

[Arwen]

Yes, with mirroring, all writes go to both disks.

On failure of one disk in a mirror, you should get an E-Mail alert. It should NOT try and reboot.

If your boot preferences are correct, it may attempt to boot off the good DOM. But, your system
board may attempt to boot off the failed DOM. This is more to do with PC hardware that x86/x64
servers came from. Unless the failed DOM is completely dead, as long as the BIOS / UFI sees the
failed DOM, and it's before the good DOM on the boot list, the failed DOM will be the boot target.

 

[STREBLO]

So you basically get fast recovery and no loss of config.

It would be nice if they could make it swap to the other drive automatically on failure.

 

[Ericloewe]

So you basically get fast recovery and no loss of config.

It would be nice if they could make it swap to the other drive automatically on failure.

Little hope of that, I'm afraid.

 

[joeschmuck]

You are correct, I misspoke and I wrote that way too early this morning.

Only the high end SSD's are SLC. Of course we all would love to have those if they were the same price as the MLC devices.

So you basically get fast recovery and no loss of config.

It would be nice if they could make it swap to the other drive automatically on failure.

Well that could be done I believe, just not using FreeNAS software. Think of a PCI-Express card like this one as and example (I'm not stating someone should do this, it's an example) and you have two M2 SATA devices in RAID 1 (mirrored) configuration. If one SSD fails then the second will still work fine. The big difference is the adapter card contains the appropriate hardware to create a RAID 1 and handle a failure but still boot the system.

So lets try a different option and I can't do this because I do not have a Supermicro motherboard to test this out but maybe you could take SATA ports 0 and 1 and in the BIOS configure these to a hardware RAID 1 (mirrored) setup. Now you could use this RAID 1 drive as your FreeNAS boot device, it would see the mirror as a single drive but if there was a failure of one of your DOM devices, it would handle the loss. What I do not know is if you can establish just the two ports as the RAID 1 and the remaining ports remain open to FreeNAS so it can run it's ZFS software RAID without issue.

Neither one of these options allow FreeNAS to control the boot device mirroring and honestly, it's likely better that way. Now this was just me thinking off the top of my head as a possible way of doing things. Think outside the box.

Hope this helps.

 

[STREBLO]

Only the high end SSD's are SLC. Of course we all would love to have those if they were the same price as the MLC devices.

Well that could be done I believe, just not using FreeNAS software. Think of a PCI-Express card like this one as and example (I'm not stating someone should do this, it's an example) and you have two M2 SATA devices in RAID 1 (mirrored) configuration. If one SSD fails then the second will still work fine. The big difference is the adapter card contains the appropriate hardware to create a RAID 1 and handle a failure but still boot the system.

So lets try a different option and I can't do this because I do not have a Supermicro motherboard to test this out but maybe you could take SATA ports 0 and 1 and in the BIOS configure these to a hardware RAID 1 (mirrored) setup. Now you could use this RAID 1 drive as your FreeNAS boot device, it would see the mirror as a single drive but if there was a failure of one of your DOM devices, it would handle the loss. What I do not know is if you can establish just the two ports as the RAID 1 and the remaining ports remain open to FreeNAS so it can run it's ZFS software RAID without issue.

Neither one of these options allow FreeNAS to control the boot device mirroring and honestly, it's likely better that way. Now this was just me thinking off the top of my head as a possible way of doing things. Think outside the box.

Hope this helps.

Interesting idea...

 

[joeschmuck]

It just depends on your requirements. If I were a server farm and I needed to keep the server up and running and a mirrored boot device was required, I wouldn't use the built in FreeNAS dual boot device option because of the hardware limitations.

 

[Ericloewe]

So lets try a different option and I can't do this because I do not have a Supermicro motherboard to test this out but maybe you could take SATA ports 0 and 1 and in the BIOS configure these to a hardware RAID 1 (mirrored) setup. Now you could use this RAID 1 drive as your FreeNAS boot device, it would see the mirror as a single drive but if there was a failure of one of your DOM devices, it would handle the loss. What I do not know is if you can establish just the two ports as the RAID 1 and the remaining ports remain open to FreeNAS so it can run it's ZFS software RAID without issue.

You'd probably need a real HW RAID controller, since PCH RAID/FakeRAID/Intel RST depends on an OS driver.

 

[joeschmuck]

You'd probably need a real HW RAID controller, since PCH RAID/FakeRAID/Intel RST depends on an OS driver.

Yea, it was unfamiliar ground for me to explore and honestly, I think I'd feel better using a true RAID card if I ever thought I needed that kind of reliability.

 

[STREBLO]

Well I guess I'll just set it up in a mirror as a sort of backup so that if my boot drive dies I can just start right back up with the other one. If I have to reboot and manually set it up I'm fine with that. I already have so two DOMS so I don't see any reason not to.