Two Raid-Arrays with ML350 E200i

[Raymond R.]

Hello,

I am using a the time beeing: 5 SAS disks 72GB within one RAID5 configuration.

The diskspace in the current configuration is almost full and I would like to add more disk capacity.

As 72GB disks are no more available (Source HP) I decided to add 3 SAS disks 147GB and with it creating a second array with RAID5 also.

I am expecting a bigger amount of total disk space than when just extending the existing raid with the same 3 additional disks.

My new configuration will be:
5 disks with raid5 with a total amount of +/- 280GB
3 disks with raid5 with a total amount of +/- 290GB.
All disk slots of the ml350 will be used.

Can you recommend this configuration and what can be expected as a change in performance?

TIA
Ray

[Michael A. McKenney]

Do you need read or write performance? The OS should be on RAID 1 along with the paging/swap file. If you need write performance, do RAID 10 over 5.

On RAID 5, going from 5 to 3 disks, you will see a drop in read performance. Basically, you have two drives with data and one parity.

You could put in a 146 or 300 GB spare drive. Set it to the 5 disk array for fail over. Remove one 72GB drive and have it fail over to the 300 GB drive, Replace that drive with a 300 GB mark it as a spare. Each day replace one 72GB drive with a 300 GB as a spare and allow the array to fail over to the new drives till all 72GB are replaced. Get good backups. Make sure the spare has failed over completed and the array is healthy. Once completed extend the array and logical partitions.

[Raymond R.]

Thanks Michael,

what you write is completely right. Thank you for your information.

In the meantime I found out that spare parts delivery service still have 72GB HDDs.

What if I change the raid5 to 7 disks. Will the read / write performance be better?

How can I (after extending the raid array) extend the file system in the ESXi 4.0.0 Server?

Regards
Ray

[Michael A. McKenney]

Reads improve up to about 8 drives in RAID 5. Writes may be slightly faster or even slower. Depends on number of writes and parity calculations. On a server than does 70%+ reads, RAID 5 is optimal. if your server does 50% writes and reads, RAID 5 will be slower. I never do RAID 5. I only to RAID 10. Not sure in ESXi how to extend the partition.

[Ali]

Hi Raymond,

Let me answer your query.

What if I change the raid5 to 7 disks. Will the read / write performance be better?

It will definately boost up the read performance. Infact read performance of Raid 5 is similar to Raid 0 Read which is considered to be the best read performance.

Write performance will not be that great in Raid 5 as there are many factors which influences your write performance in Raid 5 implementation
1. Stripe size.
2. No of disks
3. Size of the disks
4. No of writes
5. File system
6. Application type
7. Amount of controller Cache
8. BBWC
9. etc. etc.

So keepiing these factor in mind and based on your requirement, Raid 5 configuration should be made.

For example : No of writes which are smaller than a single stripe size is like a overhead for Raid 5 and result in poor write performance. This is because parity must be updated on each write.

Cache backed up with battery in HP Smart array controllers will take care of the write performance to some extent. however, chosing the correct configuration in raid 5 implementation will decide your actual Raid 5 performance.


How can I (after extending the raid array) extend the file system in the ESXi 4.0.0 Server?

What is the file system that you are talking about ext3 or vmfs?

ext3 file system : It is not possible to extend as esxi uses streamdown version of Linux kernel.

Vmfs file system : follow the steps to extend vmfs file system
1. from GUI mode (vi client) log on to the esxi host.
2. Select configuration tab.
3. Select storage option.
4. Select the required datastore properties.
5. Click on increase button under the datastore properties

hope this helps,
Thanks,
Aftab

[Raymond R.]

Thanks folks for your answers. it helped me to make a decision.

- In future I will consider Raid 10.
- I will definitely try to do the extension with one disk

Raymond