Optimal 2-Channel SCSI LVM Config

[Joseph Hoh]

This is a long post, but ANY help would be appreciated.

I have a Dell External SCSI enclosure with 14 x 146GB 10K Ultra 320 disks. It is configured with a split backplane and connected to a RP7420 with two SCSI C1010 Ultra160 Wide LVD A6828-60101 controllers - one on each of the split busses.

We need to configure this storage as a temporary holding place (2 months) for a QA Oracle environment holding several (10) OLTP and one Data Warehouse databases totaling about 700GB.

I currently have all 14 disks configured into a single VG with two PVGs - one for each of the controllers. A single 800GB mirrored LV has been created with the policy set to separate PVG, and the performance is less than optimal.

What would a better configuration be? I thought that spreading the load across 7 disks with reads and writes in parallel would give us pretty good performance, but we seem to be having some performance issues - about 10 times slower than a 2-disk mirror.

Are there kernel parameters to be tuned for such a config?

[Joseph Hoh]

Also,

Mount options, VxFS options, and LV/VG paramerters are open to adjustment.

[curt larson_1]

place tables and indices on different disks
place logfiles on a seperate group of disks
place tables that are accessed concurrently on different disks
place temporary disk areas (used for sorting) on seperate disks
stripe large tables across multiple disks
don't stripe indiscriminately
don't use lvm or hardware striping and database striping together
lvm mirroring is typical more efficient that database mirroring
database striping maybe better then lvm striping


the only kernel parameters are usually
dbc_max_pct, ebc_min_pct, bufpages, and nbuf
which apply to the amount of buffer cache memory that is allocated. check to see that this is sized appropriately.

vx_ncsize, vxfs_ra_per_disk which usually don't need to be changed and vxfs_max_ra_kbytes which for applications where there are many large sequential i/o's, it might be useful to increase this value