topic Re: 12H diskarray and JFS in Disk Enclosures

12H diskarray and JFS

Michael Salazar — Fri, 15 Feb 2002 00:06:29 GMT

Hi,
I have a fresh new L box with a 90GB 12H diskarray, and online JFS. The L box contains four separate 18.2 GB disks.

My plan???

1, Create 2 or 4 LUN???s on the 12H for our application & data VG01

2, Mirror one pair of system disks for VG00 (/ /stand /swap /usr /opt /home /etc ???)

3, Mirror the second pair of system disk as a JFS snapshot volume for application & data (disk array), while archiving to an LTO.

My questions..

1, Dose the JFS snapshot volume have to be in the same VG that I???m snapshoting?

2, When I cerate a VG on the array will I get better performance if it spans more then one LUN, even though I have two controllers and the raid is already striping?

3, We plan to expand in the future and I want to use only 2 LUN???s to start, will it be a major performance hit not using 4?

The Primary goal is to maintain data integrity on a 24X365 financial system, while maximizing performance.

Thanks in advance.

Re: 12H diskarray and JFS

Bill McNAMARA_1 — Fri, 15 Feb 2002 10:23:22 GMT

1, Dose the JFS snapshot volume have to be in the same VG that I???m snapshoting?

No.. but it needs to be the same size as the FILESYSTEM (built on an lvol)
At MAXIMUM.

It depends on how long your backup takes and how much of the files change within that period. I've always got away with 20% original size.

See bdf.

I'll try to answer your others in a sec...

Re: 12H diskarray and JFS

Bill McNAMARA_1 — Fri, 15 Feb 2002 10:27:36 GMT

2, When I cerate a VG on the array will I get better performance if it spans more then one LUN, even though I have two controllers and the raid is already striping?

Not really no.. but you will if the autoraid is accesses by the two controllers on two different busses.

ie: two PVs (luns) in your VG
access PV1 through ContrX
access PV2 through ContrY

Create a Striped LV across the two
lvcreate -i 2 -I 64 -L MB VG
newfs -F vxfs /dev/VG/LV

The cp stuff across

iostat -t 3
to see io performance.

Play around a bit..

Add alternate paths to the PVs, but avoid accessing all luns through just one controller.

If you look at my user profile here, go to the answers section, you'll find more detail on autoraid config I answered on if the above doesn't make sense..

Re: 12H diskarray and JFS

Bill McNAMARA_1 — Fri, 15 Feb 2002 10:31:20 GMT

3, We plan to expand in the future and I want to use only 2 LUN???s to start, will it be a major performance hit not using 4?

Quite the reverse.. one trafic is started on the 12h it'll start shifting data around as space fills up.

Perf hits when you use near max space and get laid in R5.

I've heard that the autoraid likes to manage 4 luns in its maps but I very much doubt that you'll notice any pb only using two...

I also heard it prefers 6 36G drives versus 12 18G drives, which also confused me a bit..

mm, strange little array, but you got to love it when you're short on space..

Later,
Bill

Re: 12H diskarray and JFS

Bill McNAMARA_1 — Fri, 15 Feb 2002 11:19:48 GMT

just to add:
Re:

The Primary goal is to maintain data integrity on a 24X365 financial system, while maximizing performance.

Well the AutoRAID isn't really a 24x7x365 array. F/W upgrade for example will require downtime. The backplane itself is a SPOF, Replacing anything at the back (SCSI) requires host downtime (to avoid potential panic).. If I were you, I'd consider a more robust array like the FC60 or better still, an XP48.
Both are pretty scalable..

Later,
Bill

Re: 12H diskarray and JFS

Insu Kim — Fri, 15 Feb 2002 12:01:47 GMT

From performance optimizing standpoint,

Factors that directly influence disk array performance.
1. Amount of available RAID 0/1.
The more RAID 0/1 space available, the better the disk array performance.
Enabling Hot spare will allow you to have more RAID 0/1 space.
2. Proper disk module installation.
Installing the disk modules in the correct slots in the enclosure distributes the disks across the internal SCSI busses and balances the I/O load properly. Disk modules should be installed from left-to-right, top-to-bottom.
3. Keep the disk capacity small ??? Having twelve disks with smaller capacities will improve the performance as compared to having twelve disks with larger capacities.

Hope this helps,

Re: 12H diskarray and JFS

Bill McNAMARA_1 — Fri, 15 Feb 2002 16:38:55 GMT

Insu,
Re point 3,

3. Keep the disk capacity small ??? Having twelve disks with smaller capacities will improve the performance as compared to having twelve disks with larger capacities.

from a techy point of view this is true, but I was told by WTEC quite the reverse.
bigger disks and less of them is recommended.
However, this is possibly more due to expansion reasons.. to increase physical disk space you don't want to pull one out to slot in a bigger one.
Remember too that the 12H needs disks of larger capacity added in pair before you benefit from the addition.

I recommend using 10 slots (not the lower 2 = closer to heat source) so that if you want to upgrade you have 2 free slots.

But on upgrade you may need to change fans if moving to a higher RPM mech.

Later,
Bill