Is it ok to put SLOG on separate HBA to data disks?

[Brezlord]

On my server I have two LSI SAS9211-8i HBAs and I would like to create a data pool with 8 4TB disks in a RAIDZ2 on one HBA and on the other HBA have the SLOG. Is there any issues to having the SLOG SSD on a separate HBA to the data disks?

Thanks,
Simon

 

[Arwen]

No, their is no problem having a SLOG disk on a separate controller.

In someways it's even best to split up your data disks across controllers. That's one nice thing about ZFS, (and most software RAID), you can use whatever interfaces are available for your server. Including mixing SAS PCI card ports and built in SATA ports, (preferably Intel type, not Marvell).

That said, in rare cases it's not a good idea. Specific example. Assume you have 2 identical SAS HBAs, (like you stated). Then have 2 non-identical PCI slots. One is an 8 lane physical & electrical. But the other is only a 1 lane electical, but open ended. Thus, putting 7 data disks & SLOG on one card in the 8 lane slot, and the last data disk on it's own sort of dedicated card in the 1 lane slot would be appropriate. It basically depends on the math of throughput.

This is why server engineers / server arch. make the big bucks.

Edit: Clarified my no answer to the original poster's message not title.

 

[Stux]

Of course, you could just use a motherboard Sata port too, assuming it's a Sata ssd.

 

[Brezlord]

Thanks for the replies.

Both PCI slots are the same type. I could most likely do away with the SLOG now that I'm going to move the ESXi data store to a 1TB Mirrored hardware RAID thats built into the mother board. FreeNAS will be just for file storage consisting of 8 x 4TB WD RED drives in a RAIDZ2. But I all ready have the Intel DC3500 SSD that I have over provisioned to 8 GB so I might as well use it.

RAID Controller in Slot 4 - PCI Device
BusNumber 9
DataBusWidth 4x or x4
Description 6Gbps SAS HBA Adapter
Device Type PCIDevice
DeviceDescription RAID Controller in Slot 4
DeviceNumber 0
FQDD RAID.Slot.4-1
FunctionNumber 0
InstanceID RAID.Slot.4-1
LastSystemInventoryTime 2017-09-21T17:54:57
LastUpdateTime 2017-09-08T18:35:47
Manufacturer LSI Logic / Symbios Logic
PCIDeviceID 0072
PCISubDeviceID 1F1C
PCISubVendorID 1028
PCIVendorID 1000
SlotLength Long Length
SlotType PCI Express Gen 3 x8
---------------------------------------------------------------
RAID Controller in Slot 6 - PCI Device
BusNumber 8
DataBusWidth 4x or x4
Description 6Gbps SAS HBA Adapter
Device Type PCIDevice
DeviceDescription RAID Controller in Slot 6
DeviceNumber 0
FQDD RAID.Slot.6-1
FunctionNumber 0
InstanceID RAID.Slot.6-1
LastSystemInventoryTime 2017-09-21T17:54:57
LastUpdateTime 2015-01-29T03:55:10
Manufacturer LSI Logic / Symbios Logic
PCIDeviceID 0072
PCISubDeviceID 1F1C
PCISubVendorID 1028
PCIVendorID 1000
SlotLength Long Length
SlotType PCI Express Gen 3 x8