What to do with my SSD? Use in iSCSI or NFS

[fips]

Hi,
my setup:
I have a Supermicro X10SL7-F, a case with 12 Slots, 8x 1TB SAS, 1x 120GB DC SSD, and 3x 2TB SATA.
Originally I wanted to create a raidz2 with that 8 SAS disks, and a simple raidz1 with that 3 SATA disks (its not an important pool).
The raidz2 SAS pool will be connected to a cluster of proxmox servers via iSCSI.
So, what to do with that SSD.

What I could read so far is, that the SSD ZIL can be very helpful for synchronous writes.
Does it mean, that the SSD ZIL is completely useless if I use it with my raidz2 SAS pool and iSCSI?

Somehow I don't want to spent a good SSD for that simple backup pool ;-)

 

[Stux]

I would think that you could partition it and add it to both pools with some command line juju

 

[Mirfster]

1x 120GB DC SSD

Is this the Intel DC S3500 Model or other?

The raidz2 SAS pool will be connected to a cluster of proxmox servers via iSCSI.

RaidZ2 and iSCSI is not really a good idea, you would want to do Mirrors

What I could read so far is, that the SSD ZIL can be very helpful for synchronous writes.
Does it mean, that the SSD ZIL is completely useless if I use it with my raidz2 SAS pool and iSCSI?

It is recommended that "sync=always" is set for iSCSI

 

[fips]

Is this the Intel DC S3500 Model or other?

RaidZ2 and iSCSI is not really a good idea, you would want to do Mirrors

It is recommended that "sync=always" is set for iSCSI

SSD is a Samsung SM863.

Why is RaidZ2 and iSCSI no a good idea? How would it be optimal?

 

[Mirfster]

SSD is a Samsung SM863

Not familiar with that SSD, but what I saw regarding it shows that is does have Power Loss Protection. Not sure about the Total Writes it can handle though. Maybe others can elaborate on it.

Why is RaidZ2 and iSCSI no a good idea? How would it be optimal?

RaidZ2 will provide basically the IOPS of one drive for each vDev. I am assuming you are only going to have a single vDev, so result is the performance of one drive...

With Mirrors you will get more IOPS resulting in more Speed; but would be a reduction in Space and some in Redundancy. However, if you were to do 3-Way Mirrors, that would help with Redundancy but result in less total Space.

Currently, I am running iSCSI for ESXi and Hyper-V VM Datastores with:

• 5 x HGST SAS 4TB Mirrors (10 Disks)
• 2 Hot Spares
• 1 Cold Spare
• A SSD SLOG (Intel DC S3710 200GB)
• L2ARC TBD (if needed)

Also, with iSCSI you don't want to go above 50% Storage Utilization otherwise performance really tanks.

Honestly, my setup results in ~17.5TB of Usable Space; but I plan on never going above 8TB combined for my iSCSI Volume (Has two zVols). Currently I have each zVol set to only 2.5TB, but can increase it to 4TB later if needed. *** From my understanding while one can increase a zVol; you don't want to try and decrease it...

So in conclusion while I have 40TB of Raw Space (10 x 4TB), which yields me ~17.5TB Usable Space (Mirror vDevs); I will only plan to ever use 8TB of that... *** Not counting the 2 Hot Spares or 1 Cold Spare

Search the Forums for info on iSCSI by @jgreco and you should see some very informative postings. After going through all that, ask yourself if you really want to do iSCSI?

The fun beings when designing a Pool/Volume and trying to find the balance between Space, Speed and Redundancy... ;)