Feature

Ford's storage ledger balances capacity decisions

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Backup storage ledger

The backup ledger is the most complicated ledger; Ford Motor Company is currently in the process of rolling out this ledger. Backup capacity isn't as straightforward as NAS or SAN capacity. For NAS and SAN capacity, the actual amount of storage is the dominant key performance indicator (KPI). But for backup, the amount of storage is just one of many criteria that must be tracked. Ford uses a progressive incremental backup approach, meaning that after an initial full backup only changed files are backed up. The team couldn't create a forecasting ledger without first understanding the backup system design criteria.

The first step in creating a backup forecast strategy is to develop criteria to address design tradeoffs, otherwise the backup systems could inadvertently slip into sub-optimal performance. The team developed the following design criteria:

  • Daily backup disk pools are large enough to contain a single day's worth of file system incremental backup.
  • Weekly backup disk pools are large enough to contain one week's worth of backup data before it's pushed to tape.
  • Database size shouldn't exceed 60 GB (to ensure that DR recovery targets can be met).
  • Data migration infrastructure must be able to dump disk pools to tape within four hours.
  • Server backups will be co-located to dedicated

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  • tapes.
  • Workstation backups will be co-located to dedicated tape groups.

For the daily incremental disk pool, a 14-day high-water mark of the disk pool average is derived and then averaged with all of the servers in that same environment. For example, assume there are 10 backup servers at a data center, each disk with 500 GB of disk pool for an aggregate disk pool of 5,000 GB. The 14-day average of each of the 10 servers is 350 GB (aggregate of 3,500 GB). The aggregate high-water mark backup capacity shouldn't go above 90%, so additional disk pool capacity should be provided before the 90% threshold is reached. Therefore the capacity is 5,000 GB times 90% minus 3,500 GB or 4,500 GB minus 3,500 GB = 1,000 GB of available aggregate disk pool.

It should be noted that there's a difference between capacity forecasting and day-to-day tuning and monitoring. Capacity forecasting is used primarily to determine future infrastructure capacity requirements; efficiently balancing current infrastructure should be a normal part of a storage admin's tasks.

The ledger's bottom line

Ford Motor Company's data storage forecasting and purchasing meetings are now more effective and collaborative, which helps ensure that the right amount of infrastructure is delivered at the right time. Storage forecasting capacity meetings are now data-driven and leverage dynamic what-if scenarios that can be created instantly. If there are questions on source data, stakeholders can quickly view ledger or spreadsheet data for more information. The ledger process also allows Ford and its IT service providers to work together better to ensure that capacity is tracked and forecasted appropriately. Any organization can implement new technology, but what truly makes a difference is how the organization adapts its actions to maximize the return on the investment.

BIO: Tom Woods is currently global ITIL services transition manager at Ford Motor Company. At Ford, Tom has held storage operations, engineering and architecture positions, and has supervised the backup and NAS teams.

This was first published in January 2010

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