A Thin Image S-VOL (snapshot) contains data stored in the P-VOL and the pool. A ShadowImage S-VOL is created by copying all P-VOL data.
The following table summarizes the volume and other differences between Thin Image and ShadowImage.
| Item | Thin Image | ShadowImage |
|---|---|---|
| Initial copy operation |
Not required. Volumes can be copied faster. |
Required. |
| Number of S-VOLs per P-VOL | Up to 1,024 | Up to 9 |
| Capacity efficiency | High. Only differential data is copied from the P-VOL. | Low. The entire P-VOL is copied. |
| Operation of copied volumes | Always used with the P-VOL. | Can be used separately from the P-VOL. |
| P-VOL physical failures | S-VOL data cannot be guaranteed. | P-VOL data can be restored using the S-VOL. |
| S-VOL or pool physical failures | If a physical failure occurs in a pool*, data in all S-VOLs that use the pool cannot be guaranteed. | If a physical failure occurs in an S-VOL, data in the S-VOL cannot be guaranteed. |
| *When a pool is full (the depletion threshold is exceeded in a pool for which the capacity for Thin Image pairs is limited), data in all S-VOLs using the pool cannot be guaranteed. | ||
The following figures explain the relation of data when a failure occurs in the P-VOL.
Thin Image S-VOLs reference data in the P-VOL. Therefore, if a failure occurs in the P-VOL, data in all S-VOLs under the P-VOL is lost.
ShadowImage S-VOLs retain all P-VOL data. Therefore, if a failure occurs in the P-VOL, data in the S-VOLs is not lost.
The following figure explains the relation of data when a failure occurs in a pool.
Thin Image S-VOLs reference data in the pool. If the pool cannot be used because a failure occurs in the pool or the pool becomes full, data in all S-VOLs that use the pool is lost. In addition, if a pool failure occurs or the pool becomes full during restoration, data in the P-VOL which is being restored cannot be used.
The following figure explains the relation of data when a failure occurs in an S-VOL.
For ShadowImage, each S-VOL independently retains data. Therefore, only data in the failed S-VOL is affected. In addition, if a failure occurs in an S-VOL during restoration, data in the P-VOL which is being restored cannot be used.