12 Drive: SAS and SATA Mix

[fips]

Hey!

i ordered a chassis with 12 bays and now i am thinking about how to build it up most efficient and safe.
Board would be a Supermicro X10SL7-F with 8 SAS Ports and 6 SATA Ports.

Thanks to the great noob ppt from cyberjock i know 11 drives would be better together with raidz3.
I guess its not a good idea to mix SAS and SATA drives in the same VDev.
But wouldn't it be sad to not use SAS? If its already exist.

It will be a NFS storage for OpenVZ.

What is the better solution:
8 SAS raidz2 (i guess still better raidz3 or?) and another pool with 4 SATA drives.
Or
11 Sata raidz3 (and hope that hot spare will be available soon)
Or
?

Best wishes

Steve

 

[solarisguy]

Not 8 +4!

6 SAS raidz2 and 6 SATA raidz2 (SAS for faster, SATA for more storage)

 

[fips]

Not 8 +4!

6 SAS raidz2 and 6 SATA raidz2 (SAS for faster, SATA for more storage)

OK, understood.
But SAS and SATA in separate pools or?

 

[cyberjock]

You absolutely can mix SAS and SATA. You'll lose some of the benefits of a full-SAS pool, but if you just want storage to have storage, mixing them isn't a bad idea.

There's lots of talk that putting SATA drives on SAS controllers can be bad, but I've had no problems on my M1015. If you plan to put SATA on SAS drives do some Google searching and see if anyone has had any problems with whatever HBA you plan to use.

An 11 disk RAIDZ3 is totally doable. You could also do 2 smaller pools, or 2 vdevs of 6 disks in RAIDZ2. It's really about personal preference.

Good luck!

 

[solarisguy]

Yes, I meant two separate pools, since I understood that in your case (OpenVZ) you can have two separate pools of data. Then you can designate the SAS pool to those clients that need a little bit more speed (or have the SAS pool be the one that has more simultaneous users).

ZFS allows mixing of almost anything, but very few combinations are meaningful and for the most (all?) scenarios identical devices in the pool give the best benefits. SAS and SATA can be mixed, but SAS-only pool should be faster (depends also on speeds of controllers and their connection to the system).

P.S. I just looked at the Amazon, and was surprised to see 4TB SAS drives at the prices I paid for the quality 4TB SATA not too long ago.

 

[fips]

This is my point.. price of SAS drives not too much in comparison with SATA.
I all the time ask myself why not to use 8 times SAS for a fast pool.
To be honest i cannot compare if to use 8 disks for raidz2 really that much worse than 6 disks...
or 7 disks in raidz3...
i have to order disks but so far i am not sure which is the best way...

 

[aufalien]

Keep in mind they are whats known as Near Line SAS, not real SAS. They have the SAS controllers with the SATA internals.

Real SAS run at a much higher RPM, lower latencies, higher MTBF rates and don't currently come in those higher SATA densities. There are also other features that you can tweak in SAS drives manually for performance which aren't available in SATA.

In a raid setup, its unclear if NL SAS performs better then SATA but you'd think that due to SAS protocol efficiencies that it would. Still, no real hard evidence.

 

[solarisguy]

With RAID-Z(1,2,3) you can mix and match, but due to the way ZFS was engineered, the optimal configurations for disks with either 512-byte or 4k sectors have:

2, 4, 8, 16 or 32 data drives​

raidz1 adds 1 parity disk, raidz2 adds 2 parity disks, raidz3 adds 3 parity disks, thus the optimal configurations would be

• raidz1 2+1 = 3, 4+1 = 5, 8+1 = 9, 16+1 = 17
• raidz2 2+2 = 4, 4+2 = 6, 8+2 = 10, 16+2 = 18
• raidz3 2+3 = 5, 4+3 = 7, 8+3 = 11, 16+3 = 19

Other RAID technologies might have a different number of data disks corresponding to 1, 2 or 3 parity disks.

Now, since you are ordering SAS hard-drives, i.e. they are not locally available to you, you may want to buy at least 7 SAS drives and configure them in raidz3 (7 disks).