Max RAID Group size with NL-SAS

[#1]

Hi, there.

I have a question about Maximum RAID Group size when using NL-SAS drives. I found the following spec sheet in NetApp site. But I cound't find NL-SAS in the Disy type.

Is NL-SAS SATA/BSAS/FSAS/MSATA/ATA categoly or FC/SAS group?

RAID group sizes

RAID type     Default size                                             Maximum size                                         Minimum size
RAID-DP       SATA/BSAS/FSAS/MSATA/ATA: 14         SATA/BSAS/FSAS/MSATA/ATA: 20              3
                     FC/SAS: 16                                              FC/SAS: 28
                     SSD: 23                                                   SSD: 28

I'll create an aggreate with 24 x X477A-R6 (4000GB). To calcurate usage space size, I want to know the aggreate will have 1 raid-dp or 2 raid-dp.

Controller is FAS3240, Enclosure is DS4243, ONTAP 8.12 P4 7 mode.

Thank you in advance.

Mariko

[#2 · Accepted solution]

Sorry if this comes too late...

NL-SAS drive are generally treated as SATA drives, and aggregate raidsize limit is set to 20 for RAID-DP.

Of course, a raidsize limit of 20 is very annoying for a 24 disk shelf.

Depending on your workload and performance requirements, you might want to set the hidden raid.raid_dp.raidsize.override option to true.

This will push the raidsize limit for those drives up to 28, and allow you to create a 22 or 23 disk aggregate with a single raid group.

Also, note that NetApp "4TB" disks have a real capacity of 3718 GiB (3807816 MiB).

If you go for a 23 disk RAID-DP aggregate, that's still 68.6 TiB of usable space.

[#3]

Hi, NICOLAS_MELAY

Thanks for your detailed explanation. I understand NL-SAS drive is treated as SATA.

I didn't know the hidden option. I'll consider if I use the option or go with raid group size 11 (2x11).

My question is cleared. Thanks a lot. 

Mariko

[#4]

I realy need to override the raidgroup size, but exactly where should i run this commando?

raid.raid_dp.raidsize.override true 

Regards Victor

[#5]

If your data is in any way important for you then I would strongly advise against using such large RAID groups, especially with large SATA disks. You only have two disks of redundancy and the reconstruct of a single 4TB disk may take many days (depending on filer load, I have seen 3TB disks having reconstruct times of 4 or 5 days under heavy load), so when another disk fails in that timeframe you're running completely without protection and every single-block error will lead to corrupt data. Since the difference in capacity is only about 10% I would suggest you use two RAID-DP groups of smaller size (i.e. 11 and 12 disks, with one hot spare)

if you still want to do it, make sure you understand the implications. Type the following to enable the override

NetApp> options raid.raid_dp.raidsize.override on

Regards

-Michael