2405 Disk System Performance

[Ted Ellis_2]

I am hoping to find someone who has seen something like this before. I have a new JBOD HP 2405 disk system. It has 8 - 73 GB drives, for which I have created 4 two disk volume groups. Each is effectively being used as a mirrored pair. The disk system is connected to an rp5430 server (HPUX 11i) via 2 - 2GB fibre adapters. I have vg01 and vg02 using one adapter as primary and vg03 and vg04 using the other. Now we did not get this to run at light speed... just some development space. We did notice that during the database load, vg03 and vg04 devices processed at almost 4 times the speed of vg01 and vg02. Suggestions on tuning or configuration checks much appreciated.

Ted

[Joaquin Gil de Vergara]

if you are using this for a database you must separate, datafiles, redo logs, archives... to separate traffic over disks (

other opention is crate only one vg and configure the disk in struipping.... thus traffic is balancd over all disks

[Ted Ellis_2]

will MirrorDisk support striping? Can I stripe across 4 disks and then mirror across the other 4?

[Joaquin Gil de Vergara]

yes

lvcreate with -m and -D options

see man page ;-)

[Ted Ellis_2]

ok... so I would need to create the volume group with strict allocation set first... after that seems the man page is a bit thin. If, for example, I wanted to create one large colume group with 8 disks, but also wanted to have mirror protection with striping:

lvcreate -m 1 -D -n /dev/vgxx

is that all I need to do? it would basically create the logical volume and mirror it at the same time so that 4 disk would have the principle stripe (PE) and the other 4 would have the mirror? And since the volume group was created with strict allocation it will automatically avoid placing any mirror PEs on the same disk?

If so.. that would be great!

[Brian M Rawlings]

Ted: Joaquin is right, but this is often a source of confusion.

There are two kinds of striping, block based and extent based. Block based is not supported by HP when you are mirroring via mirrordisk. Block based would be if you used lvcreate with the -i or -I options. These options are incompatible with -m mirror option (see lvcreate man page).

Extent based striping gives you no control over the block size of the stripe, but does let you write extents in a round robin fashion to the drives you specify, whether mirrored or not. lvcreate with -D ("distributed") option creates extent based stripes, and is fully compatible with the -m option for mirroring extents.

The problem is, extents are large (4M default), and don't provide much benefit from striping them for most applications or block sizes. Typical block size are in the k-byte range (8k, 16k, etc), so you are still doing many (500 to 1000) before moving to a new extent on another drive. For apps with larger block sizes (I don't know of any), this might be useful, but not for most.

Decisions, decisions. This is the case for a raid unit front-ending your JBOD. When your disks are protected with RAID (HW), now you don't use SW mirroring, and are free to use block-based striping and the -i or -I option to lvcreate. This lets you set the strip size down at the level where most apps get benefit from striping. All you need to remember to facilitate this is, you need lots (more than two) of LUNs/PVs to make striping pay off, so make lots of small LUNs, not one or two large ones.

Best Regards,
--bmr

[Ted Ellis_2]

the disks will have databases on them (average size are 10-15 GB... I can build an 8 disk volume group to increase the spindle count, and the extent based option does seem favorable to what I currently have. The fiber adapters on both ends of the disk system are 2GB, so my bottleneck at this point will be on writes to the disk. If I can improve that, we are OK. This was not purchased to be a hot-rod performer, and we are not going to buy in more infrastructure or software. We should be able to get adequeate performance with what we have...

[Leif Halvarsson_2]

Hi
If you think about a Raid solution you don't have to bother about striping and other in HP-HX. Let the Raid controller the job. For best performance create a Raid set of all 8 disks with Raid level 1+0 (striping + mirroring). Then use this for creating ordinary logical volumes as needed.

[Ted Ellis_2]

thanks folks.. think I will have a go with the extend striping and mirroring. I know RAID fairly well, but do not have the hardware/software option at the moment (budget stuff).

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