Question about drives and transfer rates?

There is some confusion as to what you refer to as blocks on a sector level and blocks in terms of blocks when RAID formatting and no NOT stripe size.

Apple Disk Utility clearly calls them Blocks for RAID formatting AND you get a choice.

Quote

The disks in a RAID set store data in chunks know as storage blocks. In the RAID Options dialog, you can set the size of the storage bocks to optimize a RAID set’s performance, and you can choose whether to rebuild a mirrored RAID set automatically.

From Wiki which might explain why there is yet another industry confusion similar to Kilo/Kibi:

Quote

Early in the computing industry, the term "block" was loosely used to refer to a small chunk of data. Later the term referring to the data area was replaced by sector, and block became associated with the data packets that are passed in various sizes by different types of data streams.

I think we need to hash out the terminology because I think that needs clarifying otherwise you will continue to argue the wrong point based on Blocks as Sectors.



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Ok here's one article that seems to suggest Stripe and Block are being used t describe the same thing:

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http://www.tomshardware.com/reviews/RAID-SCALING-CHARTS,1735-4.html
A stripe is the smallest chunk of data within a RAID array that can be addressed. People often also refer to this as granularity or block size. It can be compared to the blocks (logical block addressing - LBA) on conventional hard drives. Most RAID controllers allow the user to define her or his favorite stripe size, because it alters the performancecharacteristics of a RAID array. Typical options are 16, 32, 64 and 128 kB, but many professional RAID controllers also offer smaller stripe sizes, and some even support sizes as large as 256 kB.

So we can agree that Apple call it RAID Block Size whilst others call it RAID Stripe Size.



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As I said, I initially thought that Apple's "RAID block sizes" were RAID stripe sizes until I noticed that Disk Utility allowed choice of "Raid block size" for both RAID 0 and RAID 1 (which is not striped). This may be a bug in Disk Utility. Or Apple might have a uniquely cockamamie concept of "RAID block size".

I suggest we avoid Apple's overly creative terminology, and reserve the term "block size" for file system allocation block size.

Dennis Couzin
Berlin, Germany

Actually I'd prefer to add in caveats to future posts depending on the subject at hand. So if dealing with an Apple RAID software user then dealing with the terminology in use so as not to confuse the issue. However in some cases your suggestion is more pertinent. In each case making clear that the terminology could be referring to another possibility. To simply dismiss Apples "creative" use is wrong until we find out the rationale behind it.



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The danger with Apple's, or anyone's, overly creative terminology is that it causes nonsense. What did you mean when you wrote these sentences?

Quote
Ben King
From best performance you should set the block size to match the RAID stripe size or a multiple of the RAID stripe size.

IMPORTANT: If the block size you choose does not match the RAID stripe size (or multiple of) then it can be extremely detrimental to your write performance.

We know you meant "for" instead of "from", and if you turned the size relationship backwards that's a normal kind of error and we can fix it by changing "multiple of" to "divisor of". But what can the words

if the block size you choose does not match the RAID stripe size

possibly mean? There's one thing you're calling "block size" which you say you can choose, and there's another thing called "RAID stripe size" which the block size may or may not match. Please tell us what you mean by "block size" in that clause. You can't mean stripe size with the sentence as it is. You can't mean allocation block size not just because it is much smaller than the stripe size (since we can change "multiple of" to "divisor of" ), but also because allocation block size is not something you should be choosing.

Unless you like nonsense, which UK philosophy of the past century was very opposed to, you should not allow laxity in terminology to lead you there.

Dennis Couzin
Berlin, Germany

Dennis - really wondering what you are trying to accomplish here with all your words about someone else's use of words. Does this really require more than one paragraph?

Keep this thread as best you can on topic, least you loose everyone's interest. And this is an interesting thread.

Michael Horton
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Dennis

Rather than keep complaining to me about my contextual use of "Block" for what appears to you to be "Stripe" in SOME cases. Please direct your energies to Apple and ask them to clarify. I actually really want to know now! Perhaps they have it very wrong and we should be highlighting it to them so they can rectify it in future. Or perhaps they have a legitimate reason that will put your mind at rest.

That would be far more productive than you harping on about my allegedly "incorrect" use of a term that I have already clearly pointed out means many different things even in the field of Data Storage.

Regarding my comment "if the block size you choose does not match the RAID stripe size" this clearly does not apply in ALL cases. I don't run every type of RAID card or filesystem but was taught this is important rule to follow in the cases where you DO get to choose the filesystem "block size" or "minimum unit of disk space allocation" (not HDD Sector "The physical block size" which as you pointed out is either 512 bytes or 4096 bytes aka 4K) and the Stripe is a set of those blocks.

This covers not only Macs but other RAID systems on other OSs, standalone NAS up to enterprise storage systems. It's not a description for a singular drive or one particular type of RAID system. It's a "cover all" comment that IF and ONLY it applies to the interface of the person reading it then they will understand. If it doesn't apply to you or if it only applies in rare cases then it's covered regardless and you need not worry.

You are (in my opinion) correct to point out the inherent issues with terminology being confusing (I do it too) but the English language has MANY words that are not only spoken the same but written the same and yet mean different things!

The ONLY thing we must do it to try to put things into context when conveying our thoughts or imparting information - something I have been guilty of not doing on occasion when I thought (as you) that something was one way, when in fact it was many ways.

So please learn (as I) to cope with this and please or refrain from arguing ad infinitum when your view does not line up with the facts of the world around you.

...and apologies for the "From/For" typo - an inherent problem using an iPhone to post and not double checking.



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