I have strange problem with execution of stored procedure.
Database was running on old Dell server and everything was running fine. This server had 16 GB RAM and 6 disk on 10k, RAID 50.
After migration on new server (IBM x3650 M4,64 GB,10 disk on 10k,RAID 10), things started to get strange. Procedure that was running
just fine before (2-3 minutes), took around 18 minutes to finish.
As I don't have old Dell server anymore (fried motherboard), I started testing on other hardware that I had.
On other IBM server(x3250 M4, 8 GB RAM, 2 disk on 7,2k, RAID 1) it took 22 minutes to finish this procedure.
Then I switched to another old Dell server (8 GB RAM,6 disk 10k in RAID 5) and it took under 1 minute to finish.
I tested it on my PC (Lenovo, dual core, 8 GB, 500GB disk on 7.2k) and it run even faster, finished in 42 sec.
Those were all clean installations (except my PC) with exactly same settings (Windows server 2012, MS SQL 2012 SP1).I tried changing OS to Windows Server 2008 R2 but didn’t work ether, same results on both OS.
After running resource monitors, tracers and what not, I found out that key to slow procedure execution is in slow write into database
log file.
Reading from mdf is around 15 MB/s, writing to mdf around 12MB/s but writing to ldf was at max around 100kB/s.
Most of the time procedure is idle on mdf as it is waiting on ldf write to start new transaction.
On machines that are running fine (Dell and Lenovo PC) read/write on mdf is same, but write to ldf is around 12 MB/s.
I tried to place mdf and ldf on different disks but change was less then 1% so that didn’t work.
Is there some way to tune up writing to log?