Attachment uploads are currently disabled. This is a temporary situation and will resume as normal in the coming days.
Solved!
Go to SolutionCX3-40 Defrag Concerns
We are a new shop to an CX3-40 installed in May this year. During our migration process from another SAN we created quite a number of temporary luns and have now removed those creating fragmented raid groups. We have searched for threads on issues with defragmentation of raid groups and the process seems straight forward, but we still have concerns over data corruption.
Could the forum please confirm our game plan to defrag as valid, etc? -
1. Defrag one raid group at a time.
2. Set the rate an whatever the minimum is. (we have no time constraints to completing the defrag, but simply want to minimize i/o impact for our production applications.
3. Start the defrag process to run over the least active time periods.
Most of our luns are 300gb + and disk types of 300 15K.
We do have some luns of tb size, but very few in the raid 5 groups.
We have some very large (1+tb) luns in the sata (1 tb disk) raid groups.
It is unlikely we'll be removing luns in the future at the rate we have over this conversion, but it appears we MUST defrag to get the free space back in order. There are new luns we wish to create but do not have the contiguous space to do so until we defrag.
As I have said, the time to defrag is not a concern, only i/o impact and any risk of data corruption from the defrag process.
Thanks for any and all input.
-dl
Could the forum please confirm our game plan to defrag as valid, etc? -
1. Defrag one raid group at a time.
2. Set the rate an whatever the minimum is. (we have no time constraints to completing the defrag, but simply want to minimize i/o impact for our production applications.
3. Start the defrag process to run over the least active time periods.
Most of our luns are 300gb + and disk types of 300 15K.
We do have some luns of tb size, but very few in the raid 5 groups.
We have some very large (1+tb) luns in the sata (1 tb disk) raid groups.
It is unlikely we'll be removing luns in the future at the rate we have over this conversion, but it appears we MUST defrag to get the free space back in order. There are new luns we wish to create but do not have the contiguous space to do so until we defrag.
As I have said, the time to defrag is not a concern, only i/o impact and any risk of data corruption from the defrag process.
Thanks for any and all input.
-dl
- My experience is that if you set the rate to low you will be waiting several days for the defrag to complete. The low setting is designed to not impact production performance. I believe the defrag to be pretty safe and have never experienced or heard of anyone having problems with it. In fact what I usually do is defrag one raid group at a time but set the rate to high so I can guarantee it finishes before the morning.
If you want to be safe I would look to see if there are any FLARE patchees released which address issues with defrag. I do not know of any but take a look.
-Aaron - dl,
LUN access by hosts is not interrupted by a defrag, so whether it is a metaLUN or stand alone LUN you should not have an issues with the defrag. Since you are not under any time constraints using the Low setting is definitely your best option. Just remember to set the defragmentation priority on the RAID group before selecting the defrag button.
As far as your corruption concerns, I have never heard of or experienced myself any corruption of a LUN as a result of defragmenting a RAID group. It is a standard maintenance process on CLARiiON arrays and has been a solid feature for quite a while now.
There is no need for concern in my opinion. Set the priority to Low and defrag your groups one at a time.
Aran Allen Ward
6 Operator
•
2124 Posts
1005
0
Posted September 17th, 2008 10:00
My experience is the same as Aran's.
When we are defragging for cleanup and don't need the space any time soon we always set to low and let it take it's time. We never notice an impact to performance (which is what the low setting is designed for).
We have also never experienced any kind of corruption due to defrags. And I have done a LOT of defrags over the years!- Being still new at this forum, I'm am still trying to control the Helpful/Correct postings.
Just noticed there are points assigned according to "helpful" or "correct". In my opinion the responses were all very much worth 10 points, but alas, I have voided any opportunity to do this right thing.
In any event, we will forge forward with the defrag.
We started one today at low priority on the least active raid group. Yep, it's pretty slow, but, thanks to the responses to this thread, we have no fear of performing the function and time is not an issue.
Thanks for all the responses.
-dl - 3. Start the defrag process to run over the least active time periods
Since the defrag will run for days, you cannot run it over the least active time periods. Perhaps a weekend can be considered as such ?
AranH: why would you set the prio before starting the defrag ?
You can switch defrag priorities when the defrag is running, so if you want set it to low during the day and to medium during the night. There's no need to set it in advance.
Message was edited by:
RRR
Added AranH's name to point out that this part was meant for him Allen Ward
6 Operator
•
2124 Posts
1005
0
Posted September 18th, 2008 09:00
Not to mention the fact that it is always a best practice to know what you are doing before you do it. What if for some reason the RAID group had been set to High defrag priority in the past. If you didn't check before you started you could be affecting users before you know it.
For things like this I never like to assume I know that the settings are right. I always check before proceeding.
AranH1
2163 Posts
1005
0
Posted September 18th, 2008 07:00
AranH: why would you set the prio before starting the
defrag ?
You can switch defrag priorities when the defrag is
running, so if you want set it to low during the day
and to medium during the night. There's no need to
set it in advance.
Because a lot of people just start the defrag and forget about it. If you set the priority on the RAID group that you intend to use for the entire defrag then you don't need to worry about it after that.
Changing the settings would also require you to wake up before your business starts, connect to your corporate network and change the defrag priority before it can impact your business. For people that support businesses that span multiple time zones that is not reasonable. I am not going to wake up at 4am just to change the setting for a defrag. I would would rather set it once and let it run.