God bless the children, and RAID 10!

Yesterday I was doing some work on the computer that minimally read video raw frames from my Promise Pegasus2 R6 when it started doing a strange clicking sound. The unit gave up on that and I was left with a single dead drive. I was shocked that this could occur on a unit that is less than 30 months old on a day when I had not written work to the drive or was even playing video from the drives. I was just examining some individual DNG frames!

Promise will be sending me a new drive gratis as I had the three year AppleCare on the iMac and Pegasus2 purchase in early April 2016. I had selected RAID 10 for its combination of speed and redundancy. Rebuilding the array with a single new drive will be trivial in a RAID 10. And I can continue to use the system as usual until the new drive arrives.

I had been considering RAID 5 or 6 when I first installed the Pegasus2, but with one drive failed, you can’t do anything on the system until you replace the drive and the rebuild will take much longer. Now convinced that RAID 10 is the best choice for me.

I also found out that the Pegasus2 can be configured with 10TB Seagate Iron Wolf drives in the future so my array can go from its original 24TB to 60TB. Of course it is a costly upgrade but if I do move to a Thunderbolt 3 system in the future I can buy an empty Pegasus3 and move the 10TB drives over.


Sent from my iPhone using Tapatalk

Today I bought one Seagate Ironwolf 10TB drive to replace my failed Toshiba 4TB drive. My thinking is that I’ll convert my system from 24TB to 60TB as I’m able over time as other drives fail. The Pegasus2 RAID 10 is fast enough for my needs up to 4K.

I’m hoping when the next drive fails that I can pair the two 10TB drives in RAID 10 and start to take advantage of the increased capacity. But maybe not. I might get tired of waiting and pull some other drives out to repurpose them and fill the Pegasus2 with identical 10TB drives.


Sent from my iPhone using Tapatalk

Now convinced that RAID 10 is the best choice for me.

Rick, I'm glad to see you have seen the light. Not only are the rebuild times of large RAID 5/6 arrays painfully long, that stress on the disks makes a second failure dangerously likely! RAID 10 (or striped mirrors, for those of us in zfs land) protects your data better, and you get to keep that sweet write performance.

Jack, I wonder if you can comment on what I’d like to do when the next 4TB drive fails on my six drive RAID 10.

Case 1 rebuild with these drives
my current situation with the
10TB drive in the second slot

0–0 4TB
0–1 10TB but only 4TB available
0–2 4TB
1–2 4TB
1–1 4TB
1–0 4TB

Case 2
let’s say the drive in slot four fails

0–0 4TB
0–1 10TB but only 4TB available
0–2 4TB
1–2 4TB FAIL
1–1 4TB
1–0 4TB

Case 3 rebuild to this situation

0–0 4TB
0–1 10TB but only 4TB available
0–2 4TB
1–2 10TB but only 4TB available
1–1 4TB
1–0 4TB

Case 4 rebuild after switching the drives slot 4&5

0–0 4TB
0–1 10TB available
0–2 4TB
1–2 4TB
1–1 10TB available
1–0 4TB

If this works then the fifth drive is a mirror of the second drive and the RAID then may go from 12TB available to 18TB available. In other words I don’t need all the drives to have the same capacity, just the corresponding mirror drive must match. If I lost one or two drives per year, I’d soon get up to 30TB available space.


Sent from my iPhone using Tapatalk

Have a look overhere Rick

https://www.servethehome.com/raid-calculator/raid-reliability-calculator-simple-mttdl-model/

always try to remember that you have lies, f*ck*ng lies and statistics.
But it's a great help to give you an inside to the risk you take.

We use raid10 in our main workstation 8x4TB and multiple RAID-Z3's + hotspare in our storage servers.

You would be able to increase the size of individual mirrors to 10TB if you were using striped mirrors a la zfs, but I don't know what your controller will let you do.

Thanks, Misha. Jack the Pegasus2 likely doesn’t support ZFS. The Promise Utility doesn’t let me change that as far as I recall, but I’ll check on that later.

I think the drives are HFS+. My Mac system drive is APFS.


Sent from my iPhone using Tapatalk

I'm sure it doesn't, there is a lot involved in that. I suppose you'll just have to try it and see.

The 10TB Seagate drive arrives today but I’ll install it and rebuild the RAID tomorrow when I have time.


Sent from my iPhone using Tapatalk

Delayed the rebuild until today. Had an issue with the manual being inadequate to get me through this but Promise Support got me going. The new drive automatically was defined as Pass Through and I needed to change the new empty drive to Unconfigured so the Rebuild would kick off. That critical step isn’t mentioned in the manual, but all is well that ends well.


Sent from my iPhone using Tapatalk

According to Promise, putting a matched pair of 10TB drives in the Pegasus2 will not give me any more available storage in my RAID 10 system. The software uses the capacity of the lowest drive for all the drives when constructing the logical drive. I now have 30TB total physical drives but still only 12TB in my RAID 10 logical drive.

If I defined the system as JBOD, I’d have 30TB available. I’ll likely just buy another 4TB drive for the Pegasus2 and put the 10TB in an enclosure for TimeMachine backups.