Yesterday morning had a chat with a friend and ended up talking about SRDF and then later in the day had another interesting conference call on SRDF with a potential customer. So I really thought, today was the day I should go ahead and finish this post.
Back in April 2009 when the V-Max systems were initially launched, Storagezilla had a post on V-Max and SRDF features, he covers quite a bit of ground related to the Groups and the SRDF/EDP (Extended Distance Protection).
Here are the highlights of SRDF for V-Max Systems
- 250 SRDF Groups with Symmetrix V-Max (5874) Systems. In the prior generation Symmetrix DMX-4 (5773), it had support for 128 groups. Logically even with 2PB of storage, very seldom do customers hit that mark of 250 groups.
- 64 SRDF groups per FC / GigE channel. In the previous generation Symmetrix DMX-4 (5773), there was support for 32 groups per channel.
SRDF Consistency support with 2 mirrors:
- Each leg is placed in a separate consistency group so it can be changed separately without affecting the other.
Active SRDF Sessions and addition/removal of devices:
- Now customers can add or remove devices from a group without invaliding the entire group, upon the device becoming fully synced it should be added to the consistency group (with previous generation Symmetrix DMX-4, one device add or remove would cause the entire group to invalidate requiring the customers to run full establish again).
SRDF Invalid Tracks:
- The “long tail” – last few tracks search has been vastly improved. The search procedure and methods for the “long tail’ has been completely redesigned. It is a known fact with SRDF, that the last invalid tracks take a lot of time to sync as its going through the cache search.
- The SRDF establish operations speed is at least improved by 10X; see the numbers below in the performance data.
Timefinder/Clone & SRDF restores:
- Customers can now restore Clones to R2 and R2’s to R1’s simultaneously, initially with the DMX-4’s this was a 3-step process.
SRDF /EDP (Extended Distance Protection):
- 3-way SRDF for long distance with secondary site as a pass through site using Cascaded SRDF.
- For Primary to Secondary sites customers can use SRDF/S, for Secondary to Tertiary sites customer can use SRDF/A
- Diskless R21 pass-through device, where the data does not get stored on the drives or consume disk. R21 is really in cache so the host is not able to access it. Needs more cache based on the amount of data transferred.
- R1 — S –> R21 — A –> R2 (Production site > Pass-thru Site > Out-of-region Site)
- Primary (R1) sites can have DMX-3 or DMX-4 or V-Max systems, Tertiary (R2) sites can have DMX-3 or DMX-4 or V-Max systems, while the Secondary (R21) sites needs to have a V-Max system.
R22 – Dual Secondary Devices:
- R22 devices can act as target devices for 2 x R1 devices
- One Source device can perform Read write on R22 devices
- RTO improved with primary site going down
- Dynamic Cache Partitioning enhancements
- QoS for SRDF/S
- Concurrent writes
- Linear Scaling of I/O
- Response times equivalent across groups
- Virtual Provisioning supported with SRDF
- SRDF supports linking Virtual Provisioned device to another Virtual Provisioned device.
- Much more faster dynamic SRDF operations
- Much more faster failover and failback operations
- Much more faster SRDF sync’s
Some very limited V-Max Performance Stats related to SRDF:
- 36% improved FC performance
- FC I/O per channel up to 5000 IOPS
- GigE I/O per channel up to 4000 IOPS
- 260 MB/sec RA channel I/O rate, with DMX-4 it was 190 MB/seconds
- 90 MB/sec GigE channel I/O rate, with DMX-4 it was almost the same
- 36% improvement on SRDF Copy over FC
- New SRDF pairs can be created in 7 secs compared to 55 secs with previous generations
- Incremental establishes after splits happen in 3 seconds compared to 6 secs with previous generations
- Full SRDF establishes happen in 4 seconds compared to 55 seconds with previous generations
- Failback SRDF happen in 19 seconds compared to 47 seconds with previous generations
To read more about V-Max systems follow
To read more about SRDF systems follow