SAN impact on performance

We're going to be hosting a write intensive non-clustered application. With
cost constraints in place, we are down to two options:
Dell 2950 with 8 disks: 2 disks in RAID 1 for OS, 2 disk in RAID 1 for
tempdb/log files, and 4 disks in RAID 10 for the data files.
Dell 2950 with 8 disks and SAN: 2 disks in RAID 1 for OS, 2 disks in RAID 1
for tempdb, 2 disks in RAID 1 for log files, and using a SAN for the data
files. The remaining 2 physical disks would be used for backups. The SAN
is fiber channel with RAID 5.
Questions:
* If we use a SAN for the data files, is the best place for the log files
and temp db still locally on the fixed disks so we can leverage the RAID 1?
* Any general comments on comparing the scenarios above?
Thanks in advance,
Mark> * If we use a SAN for the data files, is the best place for the log files
> and temp db still locally on the fixed disks so we can leverage the RAID
> 1?
Since your application is write-intensive, I suggest you place log files on
RAID 1 (or 10) that are isolated from data files.

> * Any general comments on comparing the scenarios above?
Given the choice between local RAID 10 and SAN RAID 5, I would opt for local
disk. The optimal solution would be SAN RAID 10 for data on dedicated
spindles. Consider placing logs on the SAN only if RAID 1/10. Importantly,
don't share spindles with other servers on the SAN if performance is
important.
Hope this helps.
Dan Guzman
SQL Server MVP
"Mark" <mark@.idonotlikespam.com> wrote in message
news:ee0cgzD2HHA.5740@.TK2MSFTNGP04.phx.gbl...
> We're going to be hosting a write intensive non-clustered application.
> With cost constraints in place, we are down to two options:
> Dell 2950 with 8 disks: 2 disks in RAID 1 for OS, 2 disk in RAID 1 for
> tempdb/log files, and 4 disks in RAID 10 for the data files.
> Dell 2950 with 8 disks and SAN: 2 disks in RAID 1 for OS, 2 disks in RAID
> 1 for tempdb, 2 disks in RAID 1 for log files, and using a SAN for the
> data files. The remaining 2 physical disks would be used for backups.
> The SAN is fiber channel with RAID 5.
> Questions:
> * If we use a SAN for the data files, is the best place for the log files
> and temp db still locally on the fixed disks so we can leverage the RAID
> 1?
> * Any general comments on comparing the scenarios above?
> Thanks in advance,
> Mark
>
>
>|||Performance could be poor in either case with only 1 active spindle for
tempdb and logs. And in the first case you only have 2 spindles serving up
data. In SAN case RAID 5 takes a hit during writes. Biggest determinant I
think is how many disks in the RAID5 set on the SAN?
TheSQLGuru
President
Indicium Resources, Inc.
"Mark" <mark@.idonotlikespam.com> wrote in message
news:ee0cgzD2HHA.5740@.TK2MSFTNGP04.phx.gbl...
> We're going to be hosting a write intensive non-clustered application.
> With cost constraints in place, we are down to two options:
> Dell 2950 with 8 disks: 2 disks in RAID 1 for OS, 2 disk in RAID 1 for
> tempdb/log files, and 4 disks in RAID 10 for the data files.
> Dell 2950 with 8 disks and SAN: 2 disks in RAID 1 for OS, 2 disks in RAID
> 1 for tempdb, 2 disks in RAID 1 for log files, and using a SAN for the
> data files. The remaining 2 physical disks would be used for backups.
> The SAN is fiber channel with RAID 5.
> Questions:
> * If we use a SAN for the data files, is the best place for the log files
> and temp db still locally on the fixed disks so we can leverage the RAID
> 1?
> * Any general comments on comparing the scenarios above?
> Thanks in advance,
> Mark
>
>
>