Optimal Sector Size for Promise Pegasus R6

I got a Promise Pegasus R6 with 6 x 1TB drives. The Seagate ST4000DM000 4TB disks are now officially in the hardware compatibility list of the Pegasus R6. I am replacing all 6 1TB drives with 6 of the Seagate 4TB drives.
I use RAID 5 for all 6 disks. I have Mac OS X 10.8.4. I use the R6 primarily for video editing, photo editing, and storing iTunes media (lots of large HD video).

Some questions:

1. When I create the logical disk, should I use the 512 byte sector size default, or should I use the 4KB sector size?

2. In Disk Utility, one can specify the block size for the Pegasus disk. The default is 32KB. Is this block size unrelated to the sector size used to create the R6's logical disk?

3. In Disk Utility, should I use a larger block size (large than 32KB). Can I just change the block size in Disk Utility without affecting the data in the R6's logical disk?

4. For stripe size, the R6 default is 128KB. I plan on using 256KB stripe size. Yes, I know smaller files won't be spread across all the disks, but for my use (large video files, mainly), I was wondering if a larger strip size like 256KB would be better than the default 128KB.

5. Another possible approach, rather than optimizing the aforementioned parameters, is to just stick with the defaults (512 byte sector size, 128KB stripe size, and 32KB Disk Utility block size), and not worry about it, if the performance differences would be negligible, since one school of thought is that maybe the default values are better tested by Promise and might be more reliable.

I'd also like to hear from Promise Pegasus R6 & R4 users who purchased their units with 3TB or 4TB drives. Can you look at what stripe size was used by Promise?

Thanks.

I created my logical disk with 4Kb sector and 256Kb stripe size. I have 6 4TB disks in a RAID 5 array. Prior to creating my LD, I first upgraded to the June 2013 firmware, which has this fix:

" Data integrity testing FAILED with OS 10.8.X if the sector size of LD other than 512 bytes"

A Promise tech support person that I emailed with earlier said to just use the defaults since it is most tested, while another Promise tech support (this time someone I talked to on phone instead of email) said 4Kb is fine after he consulted with another more knowledgeable colleague.

So far, 4Kb secors work fine for me, but I didn't do any performance testing.

cinemaloha said:

Hi randm,

Also, could you post screenshots running the Blackmagic Disk Speed Test or other benchmarking app or just let me know what read/write speeds your getting as well as reliability.

I was reading the Pegasus Manual (PDF) and had a few questions for you since you've already upgraded.

1. On page 49, did you use 'Express Configuration' and use 'Application Type' as 'File Server' or 'Video Stream'? My projects are around 1.5 to 2 TB at times so maybe I'm not sure which option would be more efficient.
   
2. On page 88, I intended to use 256 KB stripe size as you did since I'm mainly editing HD Video but wanted to know your logic behind that and why not 512 KB or 1 MB? For me, 256 KB was the middle available and did not want to compromise read/write speeds. The 4 KB sector size was self explanatory for me since I want more efficient use of my disk drive.
   
3. On page 98, did you enable 'Read Ahead' for the 'Read Cache Policy'? The manual states that it "can increase read performance" but won't really know without real world test.

My R6 12 TB RAID 5 info:

• (6 x 2 TB Drives)
• Stripe Size is 128 KB
• Sector Size is 512 KB
• June 20, 2013 (5.02.0000.98) Firmware

Sorry if this is demanding but my research did not come up with much and your the first solid information I've come across. Thank you in advance.

Click to expand...

1. I didn't use Express Configuration. After I had put the 6 4TB drives in the R6, when I tried to run the Wizard, the Automatic and Express buttons were grayed out. Only the Advanced button was available.

Below are the steps that I used for setting up m6 6 x 4TB RAID 5 array:
------------
- Change Mac settings to not sleep (just in case it shouldn't sleep during synchronization)
- Unlock Promise Utility to allow changes
- Disk Array->Create Disk Array
- Subsystem Information->Clear Statistics
- Wizard->Advanced Configuration:
Create Disk Array:
Alias: <= I didn't enter anything
Enable Media Patrol: check (checked by default)
Enable PDM: check (checked by default)
Click on the 6 disks (from 1 to 6):
IDs of Physical Drives Selected: 1,2,3,4,5,6
Create Logical Drive:
Alias: <= I didn't enter anything for this
RAID Level: RAID5
Capacity: 20 TB (automatically changed to 20TB when I selected RAID5 above)
Stripe: 256K (default was 128 KB. Choices were 64KB, 128KB, 256KB, 512KB, 1MB)
Sector: 4KB (default was 512 Bytes. Choices were 512 Bytes, 1KB, 2KB, 4KB)
Read Policy: ReadAhead (default)
Write Policy: WriteBack (default)
Format: check (default)
Then clicked "Add", so new drive shows up in right side of GUI
Create Spare Drive:
I didn't select any drives for spare

Then, I clicked on "Submit"
After a few seconds, I got "Disk array was created successfully"
Then, I clicked on "Finish"

Synchronization took about 30 hours.
---------------

Most of my files are video and music files. I also thought about possibly using more than 256KB stripe size. I searched online and someone did some testing on an R6 and his conclusion was that stripe size didn't make that much difference, but someone else's test (not with an R6 but some other RAID device), changing stripe size can make 10% or so difference in performance. Not sure who to believe. I suppose I could have done some testing with different stripe sizes, but given that it takes 30 hours to synchronize the drive, I didn't have time/inclination to do the testing. So, I figured that 128KB was the default size, and doubling it to 256KB was a safe enough bet as opposed to "going on a limb" and assuming I should use 512KB or 1MB. I suppose if one had a lot of small files, a smaller stripe size helps (but for me, most files are larger). Anyway, without actual, definitive testing on large sizes (e.g. 512kB or 1MB), I figured 256KB was a good enough compromise.

As indicated above, I used ReadAhead and WriteBack. My R6 is on a UPS, so I'm okay using WriteBack.

Also attached is a snapshot of the Disk Speed Test. I ran this test with my R6 and a 2011 MacBook Air (still waiting for the upcoming Mac Pro to replace my old 2008 Mac Pro). You can also search online for test results for the Seagate ST4000DM000 4TB drive. It is (IIRC) a 5900RPM drive, but maybe it doesn't make much difference when in a RAID array of 6 drives (as opposed to a standalone internal drive, which would matter more). It's not as fast as the 3TB Seagate ST3000DM001, but it's still pretty good (and I like that it's cool and quiet). Also, 4TB means the data is packed more densely than a 2TB drive so the drive heads can theoretically get more data at a time. Also keep in mind that your R6 is 80% full. As you may know, the more full a disk is, the less the performance (given that each rotation of the platter delivers less data the closer you get to the center of the disk).

I don't use Final Cut Pro (plan to when I have some time to play with it and when I upgrade my old Mac Pro). This is the first time I've run Disk Speed Test. How do the numbers look based on what you've seen with the 6 X 2TB R6? I ran the test for a few minutes (not sure how long I'm supposed to run it).

cinemaloha said:

Maybe the 1 MB Stripe Size will make up for any performance decrease.

My write speed is 673 MB/s. My read speed is 592.3 Mb/s. Does it matter that it's a MBAir that we have a 25% & 20% (respectively) difference? My iMac specs in signature. I'm exactly at 78.71% capacity. My test is with 5 GB stress setting and ran it for 3 rounds of read/write. I can live with your posted speeds for more storage space - since 4K cameras are coming out weekly, I'm prepping myself for it.

Click to expand...

Is your R6 configured with RAID 5?

Please run the Disk Speed Test once you've configured your R6. I'm interested in how 1 MB stripe size does. Ideally, you'd want to run the test with 1MB stripe size and also with a smaller stripe size like 128KB or 256KB using the same hardware (4TB disks and same Mac). However, I don't know if you would want to re-create the logical drive for different stripe sizes since it takes a long time to synchronize the drives.

The previous test that I did was using a Mid 2011 MacBook Air (1.8GHz/4GB/256 GB Flash storage) with 5GB stress testing.

I reran the same test using a Mid 2013 MacBook Air (1.3 GHz/4GB/128GB Flash storage) . The Mid 2013 MacBook Air's CPU is faster than the 2011 MacBook Air. Apparently, it makes quite a big of difference for the Disk Speed Test. Below is the Disk Speed Test results with the 2013 MacBook Air.

I also have a late 2012 Mac Mini (the dual core version). I haven't tried the R6 on it (don't feel like lugging the R6 to another room at the moment).

I'm waiting for the upcoming Mac Pro to finally replace my old 2008 Mac Pro. I plan on using the R6 with the new Mac Pro.

EDIT: See the following article regarding stripe size:

http://www.tomshardware.com/reviews/RAID-SCALING-CHARTS,1735-4.html

Question: what sort of read/write numbers does 4K editing require??

Is it the 2013 MBA an i7 dual core? It's great to see the new test has improved speeds - I'm happy you tested it on another machine. This gives me more confidence in doing the 24 TB upgrade.

It's the 1.3GHz Dual-Core 2013 MBA, which is slower than the 1.7GHz. So, I would expect that R6 disk speed test performance can be better on the faster MBA (and your iMac as well).