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6 Posts
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1330
November 17th, 2006 12:00
Time to expand a raid group
Hello,
I have five 4+1 RAID-5 disk groups. Drives are 146GB/10k/FC. These raid groups service several host machines and all the LUNS are MetaLuns with their components taking an equal part out of each raid group. For example host A needs 50 GB of storage so it has a 50GB MetaLun comprised of five 10 GB LUNs with one coming from each group.
I hapen to have five more of the FC drives and would like to expand each of the above raid groups by one drive each. Furthermore I wish to stripe the data to get the best performance in the end.
Each raid group has 534.589 GB of total capacity with 87.184 GB of free capacity. My question is does the amount of 'data' in the raid group affect the time it would take to expand it by 1 disk using stripping or is it the size and number of the disks in the raid group?
As a time test I have created two 2+1 RG with 300GB/FC drives and configured a metal 20 GB MetaLun across both of them. Then expanded each one at a time with one additiona 300GB/FC drive. Each took about 20 minutes. The TOTAL CAPACITY of these raid groups is larger but had fewer disks and much less data than my production data.
Thanks in advance for any replies. I am not familiar with how to copy a raid group to a different raid group without the host knowing what you are doing but that could be an option.
I have five 4+1 RAID-5 disk groups. Drives are 146GB/10k/FC. These raid groups service several host machines and all the LUNS are MetaLuns with their components taking an equal part out of each raid group. For example host A needs 50 GB of storage so it has a 50GB MetaLun comprised of five 10 GB LUNs with one coming from each group.
I hapen to have five more of the FC drives and would like to expand each of the above raid groups by one drive each. Furthermore I wish to stripe the data to get the best performance in the end.
Each raid group has 534.589 GB of total capacity with 87.184 GB of free capacity. My question is does the amount of 'data' in the raid group affect the time it would take to expand it by 1 disk using stripping or is it the size and number of the disks in the raid group?
As a time test I have created two 2+1 RG with 300GB/FC drives and configured a metal 20 GB MetaLun across both of them. Then expanded each one at a time with one additiona 300GB/FC drive. Each took about 20 minutes. The TOTAL CAPACITY of these raid groups is larger but had fewer disks and much less data than my production data.
Thanks in advance for any replies. I am not familiar with how to copy a raid group to a different raid group without the host knowing what you are doing but that could be an option.
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mikew1
6 Posts
0
November 24th, 2006 12:00
I understand most of what you said but still have the question of expanding a large raid group by adding one disk and stripping it. All things being equal as far as disk sizes and disk speeds go. Does the amount of data written in the disk group have any affect on the time it would take to expand the raid groupd with one more disk? In other words if I have five 146GB drives in a raid group that's 85% full and expand it by one 145GB drive, will it take the same about of time as the same raid group that's only 20% full? Just trying to figure out the amount of time stripping takes and if the amount of data written on the disk has any bearing on this.
In the meantime I will do some additional research on copying or migrating LUNs and Raid Groups.
TIA
Mike
mikew1
6 Posts
0
November 24th, 2006 12:00
I understand most of what you said but still have the question of expanding a large raid group by adding one disk and stripping it. All thinks being equal as far as disk sizes and disk speeds. Does the amount of data written in the disk group have any affect on the time it would take to expand the raid groupd with one more disk? In other word if I have five 146GB drives in a raid group that's 85% full and expand it by one 145GB drive will it take the same about of time as the same raid group only 20% full? Just trying to figure out the amount of time stripping takes and if the amount of data written on the disk has any bearing on this.
In the meantime I will do some additional research on copying or migrating LUNs and Raid Groups.
TIA
Mike
DGM3
238 Posts
0
November 24th, 2006 15:00
The amount of host data that a RAID Group may contain does not impact/effect how long it takes to expand, when re-striping as outlined above. All space that is configured as LUNs on the current disks, needs to be re-striped to include the new disk, independent of what data may or may not be stored there from the host's viewpoint. Also keep in mind that as a block storage device, the array does not have visibility/context to what specific locations are part of active files vs. deleted files, etc.
What would have impact, is how much of the RAID Group is actually configured as LUNs. For example; if within the RAID Group only a single LUN of 50MB is configured, that's all that needs to be re-striped - the remaining capacity of the drives that are not part of any LUN within the RAID Group would not be involved in the re-striping.
Regards,
DGM
mikew1
6 Posts
0
November 28th, 2006 04:00
In other words if my raid group is 85% full with numerous LUNS it will take longer than 85% full with only a few LUNS? Just trying to figure out the best way to use the remaining five 146GB drives and thought expanding the existing raid groups would be the best as they are all comprised of MetaLuns.
Thanks,
Mike
DGM3
238 Posts
0
November 28th, 2006 19:00
Nope, I wasn't referring to the number of LUNs that consume space within the RAID Group. At a higher level, I was referring to how much of the RAID Group has actually be allocated into LUN(s). For example, a RAID 5 grouping of qty 5 of 146GB drives has (roughly) 584GB of useable capacity. There may or may not be LUNs configured that consume all 584GB. If for example only 50GB of the possible 584GB has been allocated into LUN(s)... the time it will take to migrate that 50GB will be much less than if all 584GB has been allocated.
Regards,
DGM
mikew1
6 Posts
0
November 29th, 2006 04:00
I think I understand. In other words if I have a raid group with 15 LUNS in assorted sizes it will take longer to expand the raid group than the same raidgroup with only 5 LUNS. This makes no difference on how much data is actually in the LUNS but rather the number of LUNS in the raid group?
One more before I close this thread if you wouldn't mind. Given the same raid group, I have 5 LUNS that consume 80% of the raid group and another identical raid group where I have 5 LUNS that comsume 15% of the raid group. Since both have the same number of LUNS and regardless of how much data is recorded in those LUNS, will the time to expand both raid groups be the same because there are 5 LUNS in each raid group?
Thanks for all your responses,
Mike