Disk Arrays
cancel
Showing results for 
Search instead for 
Did you mean: 

Write on VA process has poor performance but read is ok

Delrish
Trusted Contributor

Write on VA process has poor performance but read is ok

Hi Everybody,

I have a performance problem on write process on a VA7110.
I copied a 1.6 GB file to a LUN. I read the file from VA with â time cp /dev/nullâ and calculated the speed with the result of time command. I took 11 seconds to complete and the speed was 140 MB/s. I think that is ok But I have problem on Write speed on VA. I copied that file form that LUN to another LUN. I took 35 seconds to complete. Read process take 11 seconds to complete so write process take 35-11=24 seconds. As you I get poor performance on write process in comparison with read process. I test it again. This time I used Oracle and â iostatâ command for the tests.
I insert 1000000 object to database and monitor the IO speed by iostat. Maximume speed that iostat reported was 50 MB/s. What is you idea? attached you can find my HDDâ s logs. Any kindly help is highly appreciate
5 REPLIES
Marco Hogeveen_1
Trusted Contributor

Re: Write on VA process has poor performance but read is ok

Hi,

What does your VA config look like? How many disks do you have, are there any JBOD's connected to it.
How many space is used??

try to run
armdsp -a -r > armdsp.txt
and post it here

Marco
Delrish
Trusted Contributor

Re: Write on VA process has poor performance but read is ok

Hi Marco,

It is a VA7110 and has 14 disks.Attached you can find the information you wanted me to send.

Alireza
Vincent Fleming
Honored Contributor

Re: Write on VA process has poor performance but read is ok

I don't understand. 1600MB (1.6GB) * 2 (one for reading it, one for writing it) is 3.2GB or 3200MB. Divide by 35 seconds, and that's 91MB/s overall. Not bad for 14 disks.

Also, don't forget that you're reading from and writing to the same disks. You're making the disk heads seek back and forth with every read and write. This WILL make the unit underperform. Your writes are getting about 66MB/s according to your calculations (24 seconds for writes), but in truth, it would be faster than that because the head contention will slow down your reading.

Don't forget that you can't expect write performance to be as high as read performance - that's how drives work - they don't write as quickly as they read.

Now, I'm not saying there isn't anything you can do to increase performance - but you should have a good idea of how these things work, and set your expectations properly.

Two things to try - put the unit into RAID-1 mode - you're in AutoRAID mode. The RAID-1 mode is faster. Secondly, make SURE you're reading and writing from the controller that owns the RG (Redundancy Group). Load balancing the controllers or using the redundant controller for I/O will not produce optimal results.

Good luck,

Vince
No matter where you go, there you are.
Marco Hogeveen_1
Trusted Contributor

Re: Write on VA process has poor performance but read is ok

Hi Alireza,

The write performance you get from an 14 disks VA7110 isn't bad.
Here are a few more things that could speed up performance.
- Add more drives (add extra Disk Enclosures) which is a quite expensive solution... The more you have the higher your performance will be.
- Use the 2nd path. I see that the 2nd controller isn't used (the link is down). IO through multiple paths will be faster.
- Since you're only using a small amount of capacity of the VA I don't think changing VA mode from Autoraid to RAID 1+0 will speed up your performance. When you use less then 50% everything is written in RAID1+0

- I also saw that you have high performance mode enabled. Please, please do not use this! It will stop your maps from being written to disks. In case of power failure you might loose your data. You don't have a big performance penalty when you switch this setting to normal.

Marco.
Leif Halvarsson_2
Honored Contributor

Re: Write on VA process has poor performance but read is ok

Hi,
It is normal that you get better read performance then write performance when using a RAID system. There is always some write overhead, how much depends on the RAID level.

Your performance looks normal.