High Availability Storage Options and Their Impact on Performance

5
Ldev Count & Spindle Size
The term Ldev in this paper referrers to an MPE configured disk or volume.
The following is a list of features that MPE/iX provides which will help clarify the relationship between
the number of Ldevs and their size to the impact on performance:
Extent Striping Given a single large file, MPE/iX was designed to break up that file into extents
(chunks) and then spread each of those extents across the different disks within its
volume set (volume group) which we will refer to as "extent striping". This striping
was shown to improve file access the HP e3000 by spreading the I/O load across
multiple disks much the same way as the newer array technology does by
spreading its I/O by the use of RAID-0 features.
Asynchronous I/O MPE/iX is designed to initiate up to 8 individual I/O requests per Ldev (disk or
volume).
XM Facility XM supports multiple instances of itself for each volume set. This means that XM
single threading is greatly reduced when the HP e3000 is configured to have a
number of user volume sets.
Given the feature set listed above let's look at the advantages of using 8 separate 9Gbyte Ldevs instead of
using a single 72GByte drive.
Extent Striping With a number of Ldevs MPE will utilize its extent striping feature to improve
performance. This allows MPE to spread the access across multiple I/O paths and
drives.
Asynchronous I/O MPE/iX is designed to initiate up to 8 individual I/O requests per Ldev (disk or
volume). One big drive (72GByte) will be limited to only 8 asynchronous I/O
requests at any given time while that same disk capacity (72Gbytes) divided 8
ways allows MPE/iX to issue a total of 64 asynchronous I/O request for that given
capacity.
XM Facility The best way to take advantage of XM's support of multiple instances of itself for
each volume set is by dividing the 8 Ldevs into two or more volume sets. This will,
depending on the application's I/O characteristics, also reduce single threading on
XM resources (like the XM recovery log file).
High Availability Storage
Lets begin our description of storage by limiting our storage products to only those that are available,
purchasable and supported by HP and that work on the HP e3000. I will start off with describing entry
level storage solutions and go through the top of the line enterprise storage arrays. A good single point of
information of arrays and HA features available for the HP e3000 can be found at
http://jazz.external.hp.com/mpeha/ and in the left navigation window click on the ha & storage matrix
button.