Hardware RAID, multiple logical partitions in OS


G

Greg Barwis

I have 8 146Gb SCSI drives configured in a hardware-based RAID 1+0 array.
The OS, therefore, sees this as one ~584Gb hard drive.

I would ideally like to partition this with the operating system into two
drives - a 20Gb C: for the boot/system and application drive, and the rest
into a D: drive to hold custom applications and a SQL 2K database.

I know that with a single drive it is best to have only one partition per
disk, so the disk head doesn't need to move back and forth on the same disk
accessing multiple drives.

My question is, is there a compelling performance reason on a hardware RAID
to use the same rule of thumb? That is, would I be ill-advised to partition
the array as I've described? My theory is that if the D: drive fills up (a
remote possibility), it won't cause troubles for the OS, because that will
reside elsewhere. However, if system performance will suffer noticeably
from this configuration, I'll come up with an alternate solution.

Thanks in advance,

-Greg
 
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W

Warren Young

I have 8 146Gb SCSI drives configured in a hardware-based RAID 1+0 array.
The OS, therefore, sees this as one ~584Gb hard drive.

I would ideally like to partition this with the operating system into two
drives - a 20Gb C: for the boot/system and application drive, and the rest
into a D: drive to hold custom applications and a SQL 2K database.

I know that with a single drive it is best to have only one partition per
disk, so the disk head doesn't need to move back and forth on the same disk
accessing multiple drives.

My question is, is there a compelling performance reason on a hardware RAID
to use the same rule of thumb? That is, would I be ill-advised to partition
the array as I've described? My theory is that if the D: drive fills up (a
remote possibility), it won't cause troubles for the OS, because that will
reside elsewhere. However, if system performance will suffer noticeably
from this configuration, I'll come up with an alternate solution.

Thanks in advance,

-Greg

If SQL performance is an issue that is driving the use of Raid 10,
then I would recommend a split of the 8x14GB drives into separate
logical drives at the hardware level. To get the best write
performance for SQL, you want to a) separate the SQL logs from the SQL
data on different logical drives. and b) as you mentioned, use Raid 10
in heavy write I/O situations for the SQL data.

With 8 drives, I'm also assuming that you are using two scsi busses to
avoid bus saturation during heavy writes.

8 drives would give you 14Gb of space for the OS/Apps/SQL logs in
2x14GB Raid1 set but that may be too small for your needs. However it
will leave you with 6x14Gb in Raid10 netting 52GB for SQL data.

Warren
 
W

Warren Young

If SQL performance is an issue that is driving the use of Raid 10,
then I would recommend a split of the 8x14GB drives into separate
logical drives at the hardware level. To get the best write
performance for SQL, you want to a) separate the SQL logs from the SQL
data on different logical drives. and b) as you mentioned, use Raid 10
in heavy write I/O situations for the SQL data.

With 8 drives, I'm also assuming that you are using two scsi busses to
avoid bus saturation during heavy writes.

8 drives would give you 14Gb of space for the OS/Apps/SQL logs in
2x14GB Raid1 set but that may be too small for your needs. However it
will leave you with 6x14Gb in Raid10 netting 52GB for SQL data.

Warren

Set to soon, that should be 42GB for SQL data...
 
G

Greg Barwis

Warren Young said:
Set to soon, that should be 42GB for SQL data...

Thanks, this works nicely. They are actually 146Gb drives, so the space
should be okay. I have been unable to find anything discussing multiple
logical drives on a hardware array on the MS site, or on the Adaptec site,
so your advice is much appreciated. So if I set two drives at RAID1 and use
that 146Gb volume for the operating system *and* for the SQL logs, and set
the remaining 6 drives at RAID10 and use that 438Gb volume for the SQL data
(which is write-intensive), that will be sufficient space for my purposes.

We are using the Adaptec SCSI RAID 2200S controller, which is
dual-channel... would you recommend putting each RAID1 drive [for the OS
volume] on a different channel, and then also putting each RAID1 drive
[which will be striped to make RAID10] on separate channels as well?

thanks,

-Greg
 
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W

Warren Young

Warren Young said:
Set to soon, that should be 42GB for SQL data...

Thanks, this works nicely. They are actually 146Gb drives, so the space
should be okay. I have been unable to find anything discussing multiple
logical drives on a hardware array on the MS site, or on the Adaptec site,
so your advice is much appreciated. So if I set two drives at RAID1 and use
that 146Gb volume for the operating system *and* for the SQL logs, and set
the remaining 6 drives at RAID10 and use that 438Gb volume for the SQL data
(which is write-intensive), that will be sufficient space for my purposes.

We are using the Adaptec SCSI RAID 2200S controller, which is
dual-channel... would you recommend putting each RAID1 drive [for the OS
volume] on a different channel, and then also putting each RAID1 drive
[which will be striped to make RAID10] on separate channels as well?

thanks,

-Greg

I misread the drive sizes as being 14BG not 146....lol...anyway

If you split the drives for both sets across the two channels, bus
saturation could become a problem during heavy writes or reads against
both logical drives.

I would put both drives for the Raid1 set on channel-0 and the 6
drives for the Raid 10 set on channel-1. This will keep the bus from
becoming saturated for either of the logical drives. This leaves
plenty of bus bandwidth for the Raid 1 set and the Raid 10 set the
read/write as fast as the individual disk spindles can take it.

Warren
 

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