Re: troubleshooting slow I/O performance.

As Mark pointed out to me my math was a bit off - if you have 30TB in RAID 10 with 8 physical disks- your disks need to be even larger than 4TB (due to the 1 in 10, duh!) - where the seek time is most definitely also not going to be any faster.

Just wanted to clarify that - and say thanks to Mark for spotting that!

On Tue, May 8, 2018 at 2:17 PM, Stefan Knecht <knecht.stefan_at_gmail.com> wrote:

> Interesting. Looks like you should be getting more out of that type of set
> up than you are seeing to me too, at first glance.
>
> It's been a while since I looked into disk drives like this but it looks
> like you're running 4TB disks. Most of these have stats similar to those:
>
> https://www.disctech.com/Western-Digital-WD4000FYYZ-
> 4TB-Enterprise-SATA-Hard-Drives
>
> I haven't spend that much time looking around, but it seems to paint the
> picture that most of those spin at 7200 RPM. Which leads to a seek time of
> approx 10ms. If you're hitting the array hard enough so that you're
> bypassing any caches and other smart gimmicks (which slob is certainly
> doing) - you would be essentially limited by the seek time of the spindles
> themselves. So this sounds about right to me.
>
>
>
>
>
>
>
>
>
> On Tue, May 8, 2018 at 12:40 AM, Chris Stephens <cstephens16_at_gmail.com>
> wrote:
>
>> 8 physical disks / lun.
>>
>> Fibre Channel
>>
>> raid 10 with external ASM redundancy.
>>
>> thanks stefan!
>>
>> On Mon, May 7, 2018 at 12:12 PM Stefan Knecht <knecht.stefan_at_gmail.com>
>> wrote:
>>
>>> By path I meant how the storage is connected to the server. Fibre
>>> channel, iSCSI, etc...
>>>
>>> And I assume you mean that you have 30TB LUNs - I don't think there are
>>> 30TB physical disks. The actual number of physical spinning rusty things is
>>> the number that's important. E.g. how is your LUN made up?
>>>
>>> And of course, it's also important to know how the disks are arranged
>>> when the LUN is built - RAID 1, RAID 5 (I hope not but that might explain
>>> the issues you're seeing) RAID 10, etc...
>>>
>>> I'd say a friendly chat with the storage guy is probably in order :) It
>>> could be any number of things - but what's really key to get good
>>> performance out of bare metal drives is the number of drives you got.
>>>
>>>
>>>
>>>
>>>
>>> On Tue, May 8, 2018 at 12:08 AM, Chris Stephens <cstephens16_at_gmail.com>
>>> wrote:
>>>
>>>> ASM
>>>> 6 30TB spinning drives
>>>> type of path? we are not using asmlib or asm_fd (whatever its called).
>>>>
>>>>
>>>> On Mon, May 7, 2018 at 11:54 AM Stefan Knecht <knecht.stefan_at_gmail.com>
>>>> wrote:
>>>>
>>>>> Some details would help:
>>>>>
>>>>> - ASM or FS? Type of FS?
>>>>> - LUNs? Numbers, sizes?
>>>>> - metal? SSD? Type of path to the disks?
>>>>>
>>>>> Etc...
>>>>>
>>>>>
>>>>> On Mon, 7 May 2018, 21:00 Chris Stephens, <cstephens16_at_gmail.com>
>>>>> wrote:
>>>>>
>>>>>> We have a new 5 node 12.2 RAC system that is not performing the way
>>>>>> we want.
>>>>>>
>>>>>> The glaring issue is that "db file sequential read"'s are taking
>>>>>> ~10ms. before i lob this over to the storage administrators, are there any
>>>>>> possible areas in the clusterware/database configuration that I should
>>>>>> investigate first? i have root access to all of the nodes. is there any
>>>>>> information i can collect that would expedite the process of figuring out
>>>>>> why we have such slow I/O times?
>>>>>>
>>>>>> slow i/o was discovered by running slob. if you don't know about that
>>>>>> tool, you should. we all owe kevin a debt of gratitude. ;)
>>>>>>
>>>>>> if nothing else, i hope to learn a little more about storage than i
>>>>>> currently know (which isn't much).
>>>>>>
>>>>>> thanks for any help.
>>>>>>
>>>>>> chris
>>>>>>
>>>>>>
>>>
>>>
>>> --
>>> //
>>> zztat - The Next-Gen Oracle Performance Monitoring and Reaction
>>> Framework!
>>> Visit us at zztat.net | _at_zztat_oracle | fb.me/zztat | zztat.net/blog/
>>>
>>
>
>
> --
> //
> zztat - The Next-Gen Oracle Performance Monitoring and Reaction Framework!
> Visit us at zztat.net | _at_zztat_oracle | fb.me/zztat | zztat.net/blog/
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