Doug,

Yes, you will definitely see a performance degradation when your tier one is full.  In essence, when it gets full your lower tiered drives (the slower ones) will try to accommodate the work load.  

I'd strongly recommend re-evaluating your data progression profiles.  Try to keep your tier 1 available for your writes, and use lower tiers for your read data.  

If you need additional help with this, let me know.

We were having the same issue and modified our storage profiles which cleaned out all but about 5% in Tier 1 Raid 10 (SSD) according to Enterprise Manager under Storage Types.  However, we noticed that no data is migrating to Raid 5 in Tier 1 additionally under Disks in Enterprise Manager under SLSSD it shows that they are 99% allocated.  Any idea what's happening?  Seems like conflicting info.

Hey, thanks for the reply.  Let me take this question a little further.

If our Tier1 write is full, for both standard and fast track, but the Tier1 Reply/Read still has some room left, which leaves Tier1 with some free space over all, will the write start to cannibalize the remaining space for the reads to use for writes?

Copilot helped us figure this out.  When the array was installed it was installed with a Raid 5-9 setup in tier 1, however there wasn't enough SSDs to support that.  Therefore when data progression would run it would just kick the Raid 10 data in tier 1 down to Raid 5 in tier 2.  They changed tier 1 to be Raid 5-5 and that resolved the issue. Thanks.

I had a similar thing happen to me on several occasions - except it was in Tier 3. We have only 5 active SATA disks and the default was RAID5-9. Tier1 filled up because no data could get migrated down. Annoyingly this appears to be some sort of default, we had the same thing corrected twice on a single storage center.

When performance degradation occurrs because Teir1 gets full, and the lower tiered drives (the slower ones) will try to accommodate the work load for the writes (and the reads...)

... just how much degredation are we talking about?   Are we talking about a fractional percentage degradation in the 1% to 100% range?   Or are we talking about a performance degradation of several orders of magnitude, or hundreds of orders of magnitude?

It really depends on your disk configuration. In our environment we'd see a significant hit to I/O if Tier 1 filled up. Our Tier 1 has 11 active 15K FC disks. If that filled up then writes would be done to 5 active 7200 RPM SATA disks. Reads would still come from wherever the data lives.

One of our arrays, for example, is all 10K drives, so the differences in the tiers is essentiall just raid10 vs raid5.

During data progression, we go from writes completing in 2 milliseconds per write, to hundreds and even thousands of milliseconds per writes...  For most types of writes, the array essentially becomes un-writable.

What ways can data-progression be configured, so that data progression can occur, but not monopolize the back-end IO while it is occuring?  It is just while data progression is running that our performance degredation is unbearable.  Can data progression be limited to a single thread, instead of 5 or 8 threads, and be allowed to run whenever it needs to, instead of starting a specific time and running as long as it takes?

I believe data progression can be configured in a few ways, but the settings are hidden. You'll need to get Copilot to make those changes.