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petrak@monogram.sk
MD3000i and write perf
Feb 6 2010, 10:19 AM EST | Post edited: Feb 6 2010, 10:19 AM EST
We are experiencing problem with write performance on MD3000i over iSCSI from VMWare
2 SATA disks in raid 0 with write perf about 30MB/s
2 SAS disks in raid 0 with perf about 70MB/s
MD3000i firmware is the newest one ( 07.35.31.60 )
No disk firmwares available
Switch , VMWare and MD3000i set to use jumbo frames
With other types of raid write perfs are even worse
Read performance is around 110MB/s which is excelent but the writes ......

Are this numbers ok ?

Thanks Do you find this valuable?    
KongY@Dell
KongY@Dell
1. RE: MD3000i and write perf
Feb 11 2010, 12:02 PM EST | Post edited: Feb 11 2010, 12:03 PM EST
petrak,

What's your IO profile- IO size (4k, 8k, 16k, etc)? Is it sequential or random IO? Is this your actual workload or are you using a tool such as IOMeter? Please note that on reads depending on application and even certain IO stress tools, memory caching can take place. Therefore, you may see higher Read performance than Write performance. One method is to look at the packets/throughput at your switch to see if (in = out). You can also compare that throughput with your esxtop counters and perfmon (if you're using Windows VMs) / iostat (if you're using Linux VMs) esp disk throughput. Do you find this valuable?    

MiroPetrak
2. RE: MD3000i and write perf
Feb 12 2010, 1:05 PM EST | Post edited: Feb 12 2010, 1:05 PM EST
those numbers are from bonnie++ and diskbench when performing sequential write ( set to create several 1GB files) , there's no workload at this time, i'm performing tests to know what i can expect from MD3000i.
I've checked the utilization of switch port during test and during the read the utilization was about 80 ~ 90% so i think cache didn't take place. Strange for me is that when i have RAID 1 with 2 SATA disks directly on PowerEdge server with PERC6 write perf of this config is ~70MB/s but when i try RAID 1 with 2 SATA disks on MD3000i write perf goes down to ~15MB/s !!! That's what i don't understand ... such degradation of speed Do you find this valuable?