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What's the use of IOPS and interface througput to esimate the performance of a 10,000rpm HDD in RAID1 and RAID 5 ? Any calcuation example to illustrate this ?

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asked 11/21/2011 03:43

AXISHK's gravatar image

AXISHK ♦♦


11 Answers:
Have a look at the Raid-Calculator:

  http://www.wesworld.net/raidcalculator.html
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answered

Gugro's gravatar image

Gugro

Basics of IOPS

Frontend IOPS is the total number of read and write operations per second generated by an application or applications. These read and write operations are communicated to the disk(s) presented to the application or applications.
Backend IOPS  is the total number of read and write operations per second that a RAID/storage controller sends to the physical disks. The value of the backend IOPS is higher most of the time, because of the simple reason that a certain RAID level has a certain overhead. This overhead is called the write penalty

You need to know more about your application workload (reads / writes) and recommended RAID levels for application to understand what IOPS your application needs.

Once you determined your application IOPS requirement you can download the below calculator to determine how many spindles do you required to deliver the required IOPS

IOPS Calculator

Once you sized and implemented your LUNS based on the requirement you can use tools, such as IOMeter, to get specific, real-time performance values
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answered 2011-11-22 at 00:30:00

Shbasha's gravatar image

Shbasha

Performance has MANY factors that affect it.  Some of them include (no particular order)

* read/write ratio at host

* random vs sequential io (many hardware raid controllers can aggregate sequential writes so you don't need to pay as high a penalty for writes)

* write penalty for raid level. format is logical:physical where 1 logical random write at the host results in x number of writes in hardware:

   - Raid-0 1:1

   - Raid-1 , Raid-10 1:2 . both members of married pair need to be written to

   - Raid-5, Raid 50 1:4 read original data block, read original parity, write new data block, write new parity

   - Raid-6 1:6 read original data block, read original parity A, read original parity B, write new data block, write new parity A, write new parity B

* IO block size

* spin rate

* avg seek time.

* # of disks in raid set

* sunspots <grin>

I summarized all of this into a spreadsheet.  Sorry for lots of numbers.  Spreadsheet for educational purposes only, not meant as a guarantee
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    answered 2011-11-22 at 04:29:51

    bill1965's gravatar image

    bill1965

    One more check, what's the interface thought for the RAID card ? Does it mean the total througput from the set of HDDs should not exceed the thougput defined in the interface ?

    Thanks
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    answered 2011-11-22 at 06:36:26

    AXISHK's gravatar image

    AXISHK

    All RAID controllers will have a throttling effect of some sort, especially when handling large numbers of disks.

    These effects can be on IOPS and/or MB/s depending on the workload and on configuration of the controller. The workings of the cache and of cache-mirroring are the usual culprits here.

    Think of the controller as a funnel, if what you are tipping in the top (back-end disks) is greater than the output (front-end buses) then its going to slow things down!
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    answered 2011-11-22 at 19:20:38

    connollyg's gravatar image

    connollyg

    So, for a interface throughput of 16Gbit/s, does it mean the total througput generated from the set of HDD shouldn't exceed this value ?

    Thanks
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    answered 2011-11-22 at 22:51:40

    AXISHK's gravatar image

    AXISHK

    The disks will be the gating factor in performance the vast majority of the time.  Laws of physics can't be broken.

    I'm not saying that the interface is NEVER the culprit, but it's further down the list of suspects.
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    answered 2011-11-23 at 00:06:12

    bill1965's gravatar image

    bill1965

    @bill1965, bit of a generalism!   :-)

    SAS @6Gb/s = 600MB/s = just 15 disks @ (a very conservative) 40MB/s each
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    answered 2011-11-23 at 07:59:17

    connollyg's gravatar image

    connollyg

    tks
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    answered 2011-11-23 at 13:42:25

    AXISHK's gravatar image

    AXISHK

    @connollyg,

    It's rare that you will get 40 MBps out of a single disk with real world IO, which is typically small block random IO.

    Your car speedometer may say 140 Mph, but I'll bet you've never achieved that speed.
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    answered 2011-11-23 at 16:23:17

    bill1965's gravatar image

    bill1965

    I disagree!

    In a directly connected mode maybe.

    But behind a RAID controller, 40MB/s shouldnt be a problem, especially with modern disks capable of 90+MB/s
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    answered 2011-11-25 at 19:11:15

    connollyg's gravatar image

    connollyg

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    Asked: 11/21/2011 03:43

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