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EVA 8100 Leveling for FATA Disk Group is very slow

junmeng
Occasional Advisor

EVA 8100 Leveling for FATA Disk Group is very slow

Hi,

Has anyone experienced slow leveling for FATA disk group?

I recently had a 1TB FATA disk failure and the leveling is taking a very long time. It has been 3 days since we grouped back the replaced disk and it is only 19% completed.

Any advice? We have logged a case with HP and they are saying this is normal.
8 REPLIES
Víctor Cespón
Honored Contributor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

Do not worry about leveling, is not a critical process and it is done with very low priority.

I don't know about your case but most FATA disk groups I've seen are oversaturated (people is not aware of the real limits of FATA disks), so there's very little time to perform optimizing tasks like leveling.

Do not confuse leveling with rebuilding. One is important and done with high priority, the other is not important and can be interrupted in any moment to do more important things.
Uwe Zessin
Honored Contributor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

Leveling requires a lot of I/O and FATAl disk drives are not good at random I/Os.

> people is not aware of the real limits of FATA disks

The problem is even worse, because FATAl disk drives are bought (and sometimes even offered to a customer) as appropriate for 'noncritical' servers which 'don't need fast disks'.
.
Víctor Cespón
Honored Contributor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

Pff, just seen an EVAperf from a customer. On a FATA disk group with only 8 disks they try to perform 1500 writes per second. Of course since the disk group only can handle 200, the drive queue depth goes to 250 and the latencies skyrocket.

This also affects other disk groups since the writes to other disk groups have to wait for the ones on the FATA disk groups.

So people, please, do not try to do thousands of random writes on FATA disks, they are not suited for that kind of traffic.
junmeng
Occasional Advisor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

I have run evaperf and will be checking on the output tomorrow. Thanks for the advice!
Uwe Zessin
Honored Contributor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

> the drive queue depth goes to 250

In that case the controller firmware should not accept that many outstanding I/Os to a virtual disk in a FATAl disk group.

As you have indicated (and has been reported here on ITRC), the problem becomes even worse because value cache space is blocked for FC disk I/O.
.
Víctor Cespón
Honored Contributor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

Yes, we have also discussed this when we had customers with the 1 TB FATA drives and firmware below HP06. The controller firmware does not differentiate between I/Os to one disk group and to another, and does not take into account the time it takes to perform the I/Os.

It just sends I/Os in round-robin to all disk groups, so if the FATA disk group is already saturated or the disks are extremelly slow, the other disk groups have to wait.

Letting the controllers send 1500 writes to a DG that has only 8 disks and can only handle 200 is not going to do a favor to anyone.

I expect someone in the design team is thinking about implementing a SQST system for the disk groups, so slow disk groups get few I/Os and fast disk groups can have a higher share independently of them.
junmeng
Occasional Advisor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

"It just sends I/Os in round-robin to all disk groups, so if the FATA disk group is already saturated or the disks are extremelly slow, the other disk groups have to wait."

Hi, you stated that if the FATA disk group is saturated, the other disk groups will have to wait.

Do you have any links or HP documents that speak about this as I'm facing the same situation and I am searching for some document to show my customer that their utilization of FATA is impacting the whole EVA storage.

thanks!

Víctor Cespón
Honored Contributor

Re: EVA 8100 Leveling for FATA Disk Group is very slow

No, details of the internal workings of the firmware are not available to even people inside the company, or very often, we are under a NDA and cannot say much more, just, "it works that way" (for the moment).