I have a 2757 controller in the 810 with six (6) 4326 (36 GB) drive in
RAID 5 array. In the 7116 expansion cage, I added five (5) 4327 (70GB)
drives.
I have the six 4326 drives plus the last 4327 in ASP1. I have the first
five 4327 drives in ASP3.
This makes six 4327 drives. Above you've said you have five.
My first question is : Is the Total Queue Elements column showing all
the
I/O request to that drive over the 15 minute interval? The number of
samples taken in the 15 minute interval is 1786 (about 2 a second). My
typical values for Total Queue Elements range from 50-90 for the 15
minute
interval. Am I to assume that would translate into slightly more than 2
queue elements every 30 seconds? (70 TQE/15 min = 4,67/2 samples per
minute = 2.3)
"Total Queue Elements" is a bit of a misnomer - it shows how many
operations were oberved at the time of sampling. This includes the
operations waiting in a queue and opertion which is currnetly in progress
(if any).
By dividing "Total Queue Elements" (DSQUEL) by number of samples (DSSMPL)
you will get an estimate of average number of operations for this disk
unit at any given time.
This is described in InfoCenter articale:
http://publib.boulder.ibm.com/infocenter/iseries/v5r4/index.jsp?topic=/rzahx/rzahxqapmdisk.htm
In your case, if you have 90 for QSQUEL for a 15 minute interval, it means
that at any given time you had about 90/1786 = 0.05 operations in progress
- very low indeed.
The total number of operations processed by this disk unit over the
interval is DSRDS + DSWRS - reads plus writes (and this is a fact - not an
estimate).
Second question: Like I said, I have one 70 GB drive in ASP 1 and the
rest
are all 36 GB drive. I notice the 70 GB drive has a higher Total Queue
Element value. It would make sense that since it's a larger drive,
there's
more data on it, so more request for read/write.
Since i5/OS spreads data over all available disk units in ASP
proportionally to the size of the disk units, in average a disk of a
double size will have double operations targeted to it.
Since technical capabilities of disk units of the same technology are
about the same regardless of their size, this disk unit will have to work
that much harder.
Because of this, if you have more than moderate disk I/O load in the ASP,
it is not a good idea to mix disk units of significantly different sizes
in the same ASP.
Does this drive have to
handle request from both ASP's. The 'standard' read/write from OS/400
and
applications in ASP1 and the checksum at the RAID level for ASP3?
Yes, in general disk units in the RAID set have to handle parity
management operations for other disk units in the same RAID set - even if
they are in the same ASP. (Storage adapter which handles RAID, has no
awareness of ASPs.)
This varies depending on how parity data is located in disk units.
I thought the checksums on the IBM RAID array was contained on the first
four (4) drives of an array. So, ASP 1 has the OS/400 stuff on the
first
four and ASP 3 has the Domino stuff on it's first four.
You can tell at a glance, which disk units have parity data on them by
looking at their capacity - capacity of the units with parity is smaller.
To determine this more reliably, look at disk model number:
030: Unprotected or mirrored unit attached to a non-RAID capable
controller.
050: Unprotected or mirrored unit attached to a RAID capable controller.
070: Non-parity member of a parity (RAID) set. Full capacity.
071: Parity member of a parity (RAID) set with 16 parity members.
Fifteen-sixteenths
apacity.
072: Parity member of a parity (RAID) set with eight parity members.
Seven-eighths
capacity.
074: Parity member of a parity (RAID) set with four parity members.
Three-fourths
capacity.
078: Parity member of a parity (RAID) set with two parity members. Half
capacity.
Alexei Pytel
"We have every reason to assume that our assumptions are not without
reason".
Michael_Smith@xxxxxxxxxxxxxx
Sent by: midrange-l-bounces@xxxxxxxxxxxx
05/02/2007 09:34 AM
Please respond to
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Subject
Disk Queue Length
I was looking into performance on my 810. I was wondering if some of my
Domino applications were having problems with disk contention.
I have a 2757 controller in the 810 with six (6) 4326 (36 GB) drive in
RAID 5 array. In the 7116 expansion cage, I added five (5) 4327 (70GB)
drives.
I have the six 4326 drives plus the last 4327 in ASP1. I have the first
five 4327 drives in ASP3.
I copied the member I was interested in from QAPMDISK to another version
of
the file in my personal library and started running some SQL statements on
it.
My first question is : Is the Total Queue Elements column showing all the
I/O request to that drive over the 15 minute interval? The number of
samples taken in the 15 minute interval is 1786 (about 2 a second). My
typical values for Total Queue Elements range from 50-90 for the 15 minute
interval. Am I to assume that would translate into slightly more than 2
queue elements every 30 seconds? (70 TQE/15 min = 4,67/2 samples per
minute = 2.3)
Second question: Like I said, I have one 70 GB drive in ASP 1 and the
rest
are all 36 GB drive. I notice the 70 GB drive has a higher Total Queue
Element value. It would make sense that since it's a larger drive,
there's
more data on it, so more request for read/write. Does this drive have to
handle request from both ASP's. The 'standard' read/write from OS/400 and
applications in ASP1 and the checksum at the RAID level for ASP3?
I thought the checksums on the IBM RAID array was contained n the first
four (4) drives of an array. So, ASP 1 has the OS/400 stuff on the first
four and ASP 3 has the Domino stuff on it's first four.
Michael Smith
Technical Support and Data Center Manager
Farm Family Insurance cos.
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