Developers Guide

19 Understanding RAID with Dell SC Series Storage | 3104-CD-DS
5 Snapshots and Data Progression
Over time, an SC Series array determines the appropriate movement of data based on the frequency of
access. A snapshot is a point-in-time-copy (PITC) of a volume that provides fast recovery of data. Snapshots
do not copy the data but simply freeze the data as read only. New writes to the volume allocate new space in
the highest performing RAID level. Snapshots are integral to taking full advantage of the SC Series
architecture that is intended to use the fastest disks from a performance perspective while efficiently using
larger, slower disks to store less active data.
5.1 Data Progression
Data Progression moves data within a virtualized storage environment, between tiers and drive types, as well
as among multiple RAID levels within the same tier for a constant balance of performance and cost.
Data Progression runs every 24 hours to assess disk use and moves data to disk space that is more efficient
for the data usage. By default, Data Progression runs each day at 7 PM, but this schedule can be changed in
the SCOS settings. The storage profile applied to each volume determines Data Progression behavior.
Note: Storage profiles are associated with the volume and are used to determine how to move data most
effectively.
5.2 On-Demand Data Progression
Data Progression also moves snapshots. When a scheduled or manual snapshot is created, the data is
frozen and moved to the tier specified by the volume storage profile. When Data Progression is run outside of
the daily schedule, it is often referred to as On-Demand Data Progression (ODDP). Used by both HDDs and
SSDs, ODDP may be triggered by the volumes several times a day.
5.3 Data Progression and storage profiles
A storage profile works with Data Progression to indicate how the data for the volume is moved between tiers.
An SC Series array has several default storage profiles to choose from to accommodate most situations. For
instance, using the recommended profile allows the volume to use all tiers. Active data will progress from Tier
1, RAID 10 to Tier 1, RAID 5 as a snapshot, and then move to RAID 5 or RAID 6 in lower tiers after it has not
been accessed for a certain amount of time.