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Latest Thoughts on partitioning a raid5? Optimize for AV setting?

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Richard Dee
Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 25, 2015 at 9:01:21 pm

I am using an 8 drive new 28TB (formatted) raid from Dat Optic that is nice and quiet. It uses an Areca 1224 SAS card and converts it to Thunderbolt 2 inside the chassis.

With no data on the raid I was getting read and write speeds of close to 1100MB/sec but after putting 12TB to archival material on it the speeds are still above 900 but the AJA test does show a few frames of major slowdown.

Larry Jordan put out an article about creating 2 partitions, saying that partition 2 is good for archival and that partition 1 would always be the faster part of the raid. This is exactly this situation I need. There is also some thought against partitions on a raid 5.

Also I noticed "optimize AV" was disabled on the controller card and there is a choice of mode"1,2,or 3" read and write performance margin. buffer threshold. Any ideas on these settings?


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Rainer Wirth
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 25, 2015 at 10:29:44 pm

There is no need of partitioning a raid 5 array.
The speed loss with thunderbolt is common, you never get the theoretical speed with thunderbolt.
Partitioning doesn't result in gaining speed - not to my experience - how should this happen?

cheers

Rainer

factstory
Rainer Wirth
phone_0049-177-2156086
Mac pro 8core
Adobe,FCP,Avid
several raid systems


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Rainer Wirth
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 25, 2015 at 10:32:10 pm

Oh I forgot about the AV speed.
If you increase the read performance it is better for AV editing.

cheers

Rainer

factstory
Rainer Wirth
phone_0049-177-2156086
Mac pro 8core
Adobe,FCP,Avid
several raid systems


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David Roth Weiss
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 25, 2015 at 11:09:51 pm

I hate to diss Larry in any way, but trust me, he is NOT a storage expert, I have read many errors on the subject in his newsletters. I would imagine that even Larry would agree that storage is not exactly his strong suit. Larry?

Meanwhile, partitioning a RAID is lousy idea for several reasons, primarily because it slows reads on the RAID, which is typically your most expensive storage, and the prime objective of most RAID purchases is performance.

David Roth Weiss
Director/Editor/Colorist
David Weiss Productions


David is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro forum.


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Petros Kolyvas
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 26, 2015 at 12:29:04 am

Partitioning can have a huge effect on RAID performance for spinning disks. However, it's seek performance, not throughput.

The real trick is throwing away the rest of the space after the first partition. I've only ever done it on software arrays and never experimented with hardware arrays in the same way though it's still possible through various RAID CLIs from what I gather.

The primary technique is called short stroking (let the jokes roll in). Requisite flaccid wikipedia citation: https://en.wikipedia.org/wiki/Hard_disk_drive_performance_characteristics#S...

Basically, spinning disks read from the outside in. Short stroking limits the heads to a small section of the outer edge of the disk platters, thus dramatically increasing random seeks as the head are limited in their movement; they only need to move a fraction of the entire disk surface.

So, following that, a technique was developed where one would partition a small portion of the outer edge of each disk, leaving the rest unused/unpartitioned. In my use I would partition 100GB of a 1TB disk. This would limit the heads to move a fraction of the space they normally need to move. Again, this is only possible if the rest of the disk remains unpartitioned/unused as any access outside the "shorted" zone will reduce performance back to normal levels.

It also has little effect on single-file reads, but for multi-stream audio and video before the time of SSDs and more affordable large arrays, it was an option.

I only ever used this technique on scratch/cache disks at a time when SSDs of that size (100GB or so) were far more pricy than their spinning-disk brethren. I also haven't used it in 4 years.

One could, quite feasibly, partition the rest of the space for archival purposes, but make sure those partitions are not mounted when the high performance area is being used. However, in my opinion, SSDs at their current costs can be used for high performance arrays requiring massive IOPS, while spinning disks can be used for large media files.

In most cases though, save some hassle and just use an array of SSDs if need the kind of performance short stroking would offer.

--
There is no intuitive interface, not even the nipple. It's all learned. - Bruce Ediger


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Rainer Wirth
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 26, 2015 at 11:19:00 am

interesting.
Back to Richard's thread.
My advice:
Raid5, no partitioning, Setting of the raid for optimized read speed.

cheers

Rainer

factstory
Rainer Wirth
phone_0049-177-2156086
Mac pro 8core
Adobe,FCP,Avid
several raid systems


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Petros Kolyvas
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 26, 2015 at 12:03:00 pm

[Rainer Wirth] "Raid5, no partitioning, Setting of the raid for optimized read speed."

Agreed on all counts. Sorry for the tangent.

--
There is no intuitive interface, not even the nipple. It's all learned. - Bruce Ediger


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Simon Blackledge
Re: Latest Thoughts on partitioning a raid5? Optimize for AV setting?
on Mar 31, 2015 at 4:42:16 pm

Optimize AV use Mode 3 - This is meant exactly for this - to smooth out any spikes for AV reads.

You may see a slowdown but the streams will be smooth.

S



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