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@xxxxxxxxx>
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@xxxxxxxxx>
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@xxxxxxxxx>
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@xxxxxxxxx>
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@xxxxxxxxx>
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@xxxxxxxxx>
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
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