Array Performance and Data Protection
cancel
Showing results for 
Search instead for 
Did you mean: 

How would you spend your money - All flash shelf or base unit flash?

SOLVED
Go to solution
ron_fisher
Advisor

How would you spend your money - All flash shelf or base unit flash?

We have a CS-500 with 3.4T of flash and ~50T useable. We have used a little over half the space on it and our cache use in infosite is hovering around 50%. We have another array from the Borg so we're not pressed for space for another year likely. We also have three CS-300's with 1T of flash or less in outer offices.

I've got a number of quotes in front of me that I'll be going over with Nimble and our VAR today.

I'm leaning towards upgrading flash rather than capacity in the CS-500. The question is whether to upgrade the flash in the base unit or go with an ALL-FLASH shelf? I assume an all flash shelf is an easy add that doubles or triples useable flash with no impact on existing workloads.

Whereas a flash upgrade to 6.4T to the base unit requires removing existing 800G flash drives with 1600G fllash drives would require dumping everything out of flash somehow then going through a warm up with new?

The nice thing about the flash upgrade to the base is we can repurpose the 3.4 to one of our CS-300's... and the 1T to one of the lessers.

Flash base upgrade is a good chunk of change less costly than the all flash shelf.

7 REPLIES
Valdereth
Trusted Contributor

Re: How would you spend your money - All flash shelf or base unit flash?

The CS500 tops out at 6.4TB currently, I like the idea you present with upgrading the array cache and cascading the 3.2TB down to other units.  Upgrading cache can be done online and is nondisruptive, its crazy to see how fast the new SSD 'warms' up and gets populated with cache worthy data again.  You can find the upgrade process under the hardware section in InfoSight.

ron_fisher
Advisor

Re: How would you spend your money - All flash shelf or base unit flash?

Yeah I was told by our SE that the cache upgrade was just matter of swapping disks one by one letting them sit overnight each time for warm up. We're planning to do the 6.4 upgrade along with adding a 30T shelf... spend it while ya got it!

mgram128
Valued Contributor
Solution

Re: How would you spend your money - All flash shelf or base unit flash?

Ron,

There really is no "right" answer for every current configuration on what option to use when upgrading the SSD Flash in your Nimble array.  Its sounds like you currently have 3.2 TB of SSD in your current CS500.  Upgrading to 6.4 TB in the same shelf can be done by the method "valdereth" described.   This process is non-disruptive and if you only change out one drive ever 4+ hours, you are not likely to see much if any performance degradation on reads.  Although you could replace them one right after the other (you must keep at least one in the array to keep it running) it is not recommended as you would completely empty all cached reads and it would take a little while to refresh that data back to cache.

You can also add an All Flash Shelf non-distruptively.   An AFS adds 16 SSD slots that can be populated in 4 SSD increments.  These increments can be either 3.2 or 6.4 TB each.    When you add a AFS, you are leaving the original SSDs in the head shelf so there is no displacement of "hot" data so there is no short term read performance to be concerned about.

As for the most cost effective manner to expand SSD, it really depends on your longer range plans to expand your CS500.   The CS-500 can address up to 36TB of SSD resources.   If you upgrade your head shelf to 6.4 TB, and someday you will need more than 6.4TB, then it would be more cost effective to add the shelf now.  If you never see a need to expand beyond the 6.4 TB in your CS500, then the in-shelf upgrade makes more sense.

Mitch

ron_fisher
Advisor

Re: How would you spend your money - All flash shelf or base unit flash?

mmmm 36T of SSD... Read latency should be down where Write latency is then.. :-)

vladv106
Advisor

Re: How would you spend your money - All flash shelf or base unit flash?

Correct me if I'm wrong but isn't the flash cache a RAID0 config? If it is, removing a drive would break the stripe thus the read cache would be empty wouldn't it? In this case it may be better to remove all the SSDs and replace them without waiting.

mgram128
Valued Contributor

Re: How would you spend your money - All flash shelf or base unit flash?

Vlad, actually the SSD Cache is JBOD, but we write to it in a logged structure file system striping the data across all 4 drives so you sort of resembles RAID0 but it is not.  When you remove a drive, you simply lose the blocks in the file system that were removed, not the entire set.  As such, you really can remove a drive, wait 4+ hrs and remove the next drive, wait 4+ hrs and so on and not see much a of a performance drop.    If you shut down the array, remove all 4, install 4 new drives and power back up, the cache will be completely empty and it will take some time for CASL to learn about all your hot blocks again.

vladv106
Advisor

Re: How would you spend your money - All flash shelf or base unit flash?

Thanks for the clarification. Didn't know the subtleties of how you write to cache.