RAID 1 vs RAID 10

Which one is faster RAID 1 (on local disk drives) or RAID 10 (on a SAN)? We
are wondering what to use for the log files.RAID10 will be faster than RAID1 whether it's on the SAN or not. The SAN
should be faster than local disks, but that depends on what other systems
are also using the SAN.
"Shiva" <arbitsquare@.hotmail.com> wrote in message
news:Oj9AKs5cGHA.1208@.TK2MSFTNGP04.phx.gbl...
> Which one is faster RAID 1 (on local disk drives) or RAID 10 (on a SAN)?
> We are wondering what to use for the log files.
>|||> The SAN should be faster than local disks, but that depends on
> what other systems are also using the SAN.
SAN is not necessarily faster than local disks, and it doesn't depend on
what other systems are using the SAN. Whether you get better performance wit
h
SAN or local disks depends on how they are configured.
Conceivably, you can >almost< always configure local disks to outperform
disks presented from SAN.
Linchi
"Michael D'Angelo" wrote:

> RAID10 will be faster than RAID1 whether it's on the SAN or not. The SAN
> should be faster than local disks, but that depends on what other systems
> are also using the SAN.
> "Shiva" <arbitsquare@.hotmail.com> wrote in message
> news:Oj9AKs5cGHA.1208@.TK2MSFTNGP04.phx.gbl...
>
>|||Additionally, RAID 10 is typically only faster than RAID 1 in terms of
read performance. For writes, which transactions logs consist of nearly
100%, both are pretty close in performance. Also, since transaction
logs are sequential and the heads usually stay over the same spot on the
platters, you don't get the random I/O benefit that RAID 10 normally
gives with the striping. So a RAID 10 volume would, under most
circumstances, be no better than a RAID 1 volume for logs.
Kalen Delaney wrote a good section on RAID volumes in Inside SQL Server
2000 - worth a read. Also you can get some good ideas about disk
configuration from reading the data & log layout sections in the TCP-C
benchmark full disclosure reports on www.tcp.org (section 4.2
"Distribution of Tables and Logs" in the IBM full disclosure reports or
section 4.1 "Database Layout" in the HP full disclosure reports).
Microsoft used to use RAID1 for logs from memory but I noticed the most
recent one they had (SQL 2005 1.2M benchmark) used RAID1+0 physical and
then NT striping across those logical RAID volumes. The DB2 3.2M
benchmark and the Oracle's 1.6M benchmark both used RAID5+0 as far as I
can tell (DB2 - stripes across 10 separate RAID5 volumes, each volume
consisting of 14 spindles; Oracle - stripes across 8 RAID5 volumes, each
volume consisting of 12 spindles). So all the top benchmarks tend to
use striping of some sorts, which is interesting since for write
performance it shouldn't be any faster really than straight mirroring.
*mike hodgson*
http://sqlnerd.blogspot.com
Linchi Shea wrote:
[vbcol=seagreen]
>SAN is not necessarily faster than local disks, and it doesn't depend on
>what other systems are using the SAN. Whether you get better performance wi
th
>SAN or local disks depends on how they are configured.
>Conceivably, you can >almost< always configure local disks to outperform
>disks presented from SAN.
>Linchi
>"Michael D'Angelo" wrote:
>
>|||"Linchi Shea" <LinchiShea@.discussions.microsoft.com> wrote in message
news:3EAE716E-B80B-41E8-86BD-53C672D67935@.microsoft.com...
> SAN is not necessarily faster than local disks, and it doesn't depend on
> what other systems are using the SAN. Whether you get better performance
> with
> SAN or local disks depends on how they are configured.
> Conceivably, you can >almost< always configure local disks to outperform
> disks presented from SAN.
> Linchi
I'd be interested to see when that would be the case. If both cases have
the same disk configuration, but your local raid controller has, say, 128mb
of cache, but the SAN has a 2gb cache, wouldn't the SAN conceivable
outperform local disk?
Of course I can see if local disks or the SAN can provide more physical
disks than the other, then that would make a difference.
[vbcol=seagreen]
> "Michael D'Angelo" wrote:
>|||The most likely factor that would influence SAN disk performance would
be load applied by other hosts (mostly on the disks themselves, but also
the SAN cache & controllers). With the local disks they're always 100%
dedicated to the SQL host, but often (not always but often) the RAID
group on the SAN that you get your LUNs for SQL from will also be used
by other systems like email, other SQL hosts, file servers, VMs, etc.
Also, depending on how the cache on the SAN is configured it may not be
very useful for what SQL will use the LUN for (so that 2GB cache may be
useless). For example, if the cache is configured mostly for read, then
that's not going to help transaction log LUNs, which are almost
exclusively write only.
Most of the time I would think SAN LUNs ought to give better
performance, all things being equal, but I can see cases (and have
experienced them myself - sharing with Exchange can be a dog) where
local DAS disks can yield better performance.
*mike hodgson*
http://sqlnerd.blogspot.com
Michael D'Angelo wrote:

>"Linchi Shea" <LinchiShea@.discussions.microsoft.com> wrote in message
>news:3EAE716E-B80B-41E8-86BD-53C672D67935@.microsoft.com...
>
>I'd be interested to see when that would be the case. If both cases have
>the same disk configuration, but your local raid controller has, say, 128mb
>of cache, but the SAN has a 2gb cache, wouldn't the SAN conceivable
>outperform local disk?
>Of course I can see if local disks or the SAN can provide more physical
>disks than the other, then that would make a difference.
>
>
>
>