Server Disk I/O issue?

Question

I have a server 2008 with 24gb of RAM. On it, there are 5 separate instances; some SQL2008 and some SQL2012.
In my Oracle databases that are in Windows environment, I normally reserve 30% (about 7gb) of RAM for OS. So this is what I'm doing as well for this server.
I allocated 10% of the remaining (about 1.5gb) to the max server memory to each of the default instance, instance 2, 3 and 4.
I allocated 50% of the remaining RAM (11gb++) to the max server memory to instance1 because it has a numerous databases and one particularly huge database (> 5tb) and about 10-15k rows inserted daily.
Question 1: Is that how you allocate RAM? Based on database size and activity?
Question 2: I have a user reporting that when she has bulk insert (1000++ rows) from an 3rd party application; the application hangs and nothing will get inserted. Her database (DBXYZ) is in instance 4. Could this be related
to amount or RAMs allocated to instance 4?
Question 3: I was reading
http://www.sqlskills.com/blogs/paul/how-to-examine-io-subsystem-latencies-from-within-sql-server/ and executed the 2nd query. The read/write latency for
DBXYZ are 111 and 571 respectively. Is that too high?
Question 4: The article mentioned "read and write hot spots are and then drill into a database to see what’s going on, and if nothing out of the ordinary" - what am I suppose to drill on the database and what's out of the ordinary?
Thanks
Ami

Answer 1

Hello Ami,
1. Configuring MAX server memory for SQL Server can be done through article.
http://www.sqlskills.com/blogs/jonathan/how-much-memory-does-my-sql-server-actually-need/
Now it is an article which will give you tentative value which is almost every time correct but for configuring MAX server memory properly for  server having multiple instance you need to look at perfmon counter.Please refer to below article it has
section as 'How to test SQL Server is facing memory crunch there are perfmon counters which you have to look .If you configured memory such that Your target server memory is less than or equal to total server memory and page life expectancy is high with high
buffer cache hit ratio and low checkpoint pages/sec you can say you have configured memory well
http://social.technet.microsoft.com/wiki/contents/articles/22316.sql-server-memory-and-troubleshooting.aspx#Does_my_system_have_low_memory
11G memory for Terabyte of data seems less to me .
2.There can be many reasons for that may be blocking may be server is not able to cope with load its difficult to answer unless you provide some stats.
3.If you see Pauls answer for what is value which should be considered as good he said it depends .So please can you check perfmon counters according to this article and it has value which will tell you what is acceptable and what not
http://blogs.msdn.com/b/askjay/archive/2011/07/08/troubleshooting-slow-disk-i-o-in-sql-server.aspx
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