HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual page 125

• Use RAID 5 configuration on the EVA in order to get faster sequential access and better capacity
efficiency.
Sizing/implementation Examples
There are no standard, generic rules for sizing your environment but there are general parameters
that you can use to help you understand your capacity needs.
Example 1 VLS Sizing for Performance and Capacity
Assume that you have 12 servers being backed up across a SAN. Each is pushing data at 15 MB/sec.
You are writing to four LTO2 tape drives, which have a maximum write speed of about 60 MB/sec
with 2:1 compressible data. You are not fitting within your backup window.
Naturally, you want to use your servers, backup window, SAN, and tape drives/library as efficiently
as possible. If the servers are only backing up at 20 MB/sec, you are not streaming the LTO2 drives
and the backups are taking four times as long to complete, because you are only using the tape drives
at one quarter of their performance. You do not want to send the backups over the LAN because it
will cause LAN bottlenecks and you do not want to buy more tape drives.
Introduce VLS into your environment. How do you size the VLS in terms of performance and capacity?
The average throughput speed of the VLS 6510 base configuration is approximately 225 MB/sec,
and the aggregate throughput required by your backups is 180 MB/sec. This fits. But you have
additional options.
Now that you have determined the minimum configuration of the VLS (by making sure that the
performance of the VLS accommodates your aggregate throughput), consider how much capacity
you need to have and how you reach that. Of course this requires not only that you understand your
base storage needs (what is the size of the full and incremental backups) but that you factor in retention
policies.
For example, if each host is backing up 400 GB in a full backup and 40 GB for each incremental
backup, and if the retention policy for the virtual cartridges is to store one week of backups, and a
"week's worth" is one full and five incremental backups, then each host will require storage for 600
GB of data. This would therefore require 7,200 GB of backup capacity in the VLS. There are two
methods for achieving this. You can enable compression when you create virtual tape drives, so that
the capacity of the base VLS 6510 would be sufficient, but this would not allow for future performance
expansion (e.g., adding more hosts), since compressed performance is limited to 190 MB/sec even
if you add capacity upgrade. The alternative, if you want to allow for future performance growth, is
to leave the data uncompressed and add a capacity upgrade to the VLS 6510 to increase the capacity
to 7,500 GB (this increases the uncompressed performance as well).
Finally, you have to configure copy jobs. If you use the four-drive library for the copies, the VLS will
be able to stream the drives. Despite the fact that the copy jobs are going to fewer drives than the
backup, the copy time will be approximately equal to the backup time because you're using the drives
efficiently.
Example 2 Testing Backup to Tape vs. Backup to VLS
In this example:
• One virtual library (VLS 6105) has been configured with five drives
• Servers 1 and 2 have LAN-attached data
• Servers 3, 4, and 5 have shared storage resident on the MSA 1000
• The backup application is Data Protector
HP StorageWorks VLS and D2D Solutions Guide 125