Performance of 1 large filesystem vs. several smaller ones

[Steve Glubka]

What are the performance issues in using a single 100GB mount point vs. having 4 separate mount points at 25GB each? (I can split my data up any way I want, so it's more advantageous from an admin role to leave the 100GB mount point.) This is pointing to an Autoraid with 8 18GB disk drives.
Also, is the Raid5 on the Autoraid atrocious for writes as opposed to the Raid 0/1?

Thanx

[Ovidiu D. Raita]

I'm sure you'll get a lot of answers.

Here's one of them: If the number of files is big ( > 100,000) you'll have performance problems and defragmentation. I had once 5 million files in one FS and I needed 14 hours to copy 40MB of data from one system to another. The same amount of time I needed to Omniback FS backups.

Ovidiu

[paul courry]

Hmmmm.... I'll run where angels fear to tread.

More spindles means more theoretical I/O's per second. Each physical drive is limited to about 30 I/O's per second. Now in a Raid environment Raid 1 will get you a lot more performance than Raid 5 because your requests are spread over more controllers and handled by more drives. I will defer at this point to those who are infinitely more knowledgeable about Raid configurations than me, but for my money, take the 4 25Gb mount points than a single 100Gb mount point.

[Dragan Krnic]

I failed to understand how the situation with 5 million files would have improved by having 4 separate mount points. Would each mount point equally partake in the file pool? Or wouldn't, as is more likely, most of the 5 million files land in one of the 4 quarters? Would 4 mount points instead of one have made your system somehow more performant or what?

The size of a file system doesn't matter so much as the ability of the underlying hardware to provide as many independent concurrent accesses as possible. This means: Have as many disks as you can and build the volume in such a way that fewest contiguous blocks are on the same physical volume. In other words - stripe.

[Andreas Voss]

Hi,

The count of lvols is not so important as the count of the LUN's you have.
If your AutoRaid has two conrollers it would be better to split into more than one LUN becaue if you are using only one LUN you will have all the trafic on one controller. With more LUN's you can balance between the controllers.
I would recommend to create 4 LUN's with each of 25GB.
When creating/extending the vg use alternate the primary/alternate path of the LUN's.
Another method is to use striping accross the LUN's. This will balance the I/O between AutoRaid and host at the best.
Within your vg you can create only one lvol that now spans over the different LUN's.

Regards