Something I noticed recently that I didn’t know (not sure
this knowledge is actually that useful), is that you can have smaller data
disks in a RAID group with larger data disks, and the larger data disks are not
right-sized down to the size of the smaller disk!
The rule is that you can have data disks in the RAID group
smaller that the largest data disk, and not cause the larger data disks to be down-sized, as-long-as the parity disks are the size of the
largest data disk. The smaller disk just get truncated.
Here are a few tests/examples:
TEST 1: Create an aggregate with 5 * 113.4MB SSD and
usable size = 233.8MB
TEST 2: Add a 527.6MB SSD to the aggregate created in
TEST 1, and - as expected - the disk would be downsized
TEST 3: Create an aggregate with 6 * 527.6MB SSD + 1 * 113.4MB
SSD and usable size = 1.83GB (not 389.5MB as might have been expected)
TEST 4: Create an aggregate with 7 * 527.6MB SSD and add
1 * 113.4MB SSD
TEST 5: What happens when we try to replace the 113.4MB
SSD with a 527.6MB SSD?
Test Results
TEST 1: Create an aggregate with 5 * 86.56MB SSD and
usable size = 233.8MB
CLU01::> aggr create -aggregate
TEST_SSD2 -disklist NET-1.37,NET-1.38,NET-1.39,NET-1.40,NET-1.41
Info: The layout for aggregate
"TEST_SSD2" on node "CLU01-01" would be:
First Plex
RAID Group rg0, 5 disks (block checksum, raid_dp)
Usable Physical
Position Disk Type Size Size
---------- ------------------------- ---------- -------- --------
dparity NET-1.37 SSD - -
parity NET-1.38 SSD - -
data NET-1.39 SSD 86.56MB 113.4MB
data NET-1.40 SSD 86.56MB 113.4MB
data NET-1.41 SSD 86.56MB 113.4MB
Aggregate capacity available for volume use would be 233.8MB.
TEST 2: Add a 500MB SSD to the aggregate created in TEST
1, and - as expected - the disk would be downsized
CLU01::> aggr add-disk -aggregate
TEST_SSD2 -disklist NET-1.8 -raidgroup rg0
Info: Disks would be added to aggregate
"TEST_SSD2" on node "CLU01-01" in the following manner:
First Plex
RAID Group rg0, 6 disks (block checksum, raid_dp)
Usable Physical
Position Disk Type Size Size
---------- ------------------------- ---------- -------- --------
data NET-1.8 SSD 86.56MB 527.6MB
Aggregate capacity available for volume use would be increased by 77.93MB.
WARNING: One or more disks to be added will be downsized.
TEST 3: Create an aggregate with 6 * 527.6MB SSD + 1 * 113.4MB
SSD and usable size = 1.83GB (not 389.5MB as might have been expected)
CLU01::> aggr create -aggregate
TEST_SSD -disklist
NET-1.1,NET-1.46,NET-1.47,NET-1.48,NET-1.49,NET-1.50,NET-1.51
Info: The layout for aggregate
"TEST_SSD" on node "CLU01-01" would be:
First Plex
RAID Group rg0, 7 disks (block checksum, raid_dp)
Usable Physical
Position Disk Type Size Size
---------- ------------------------- ---------- -------- --------
dparity NET-1.46 SSD - -
parity NET-1.47 SSD - -
data NET-1.1 SSD 86.56MB 113.4MB
data NET-1.48 SSD 500MB 527.6MB
data NET-1.49 SSD 500MB 527.6MB
data NET-1.50 SSD 500MB 527.6MB
data NET-1.51 SSD 500MB 527.6MB
Aggregate capacity available for volume use would be 1.83GB.
CLU01::> aggr show
Aggregate Size Available Used% State RAID Status
--------- -------- --------- -----
------- ------------
TEST_SSD 1.83GB
1.83GB 0% online raid_dp,normal
Image: The smaller data disk doesn’t affect the usable
size of the larger data disks, it just truncates!
TEST 4: Create an aggregate with 7 * 527.6MB SSD and add
1 * 113.4MB SSD
CLU01::> aggr create -aggregate
TESTSSD3 -disklist NET-1.6,NET-1.7,NET-1.52,NET-1.53,NET-1.54,NET-1.55,NET-1.56
Info: The layout for aggregate
"TESTSSD3" on node "CLU01-01" would be:
First Plex
RAID Group rg0, 7 disks (block checksum, raid_dp)
Usable Physical
Position Disk Type Size Size
---------- ------------------------- ---------- -------- --------
dparity NET-1.6 SSD - -
parity NET-1.7 SSD - -
data NET-1.52 SSD 500MB 527.6MB
data NET-1.53 SSD 500MB 527.6MB
data NET-1.54 SSD 500MB 527.6MB
data NET-1.55 SSD 500MB 527.6MB
data NET-1.56 SSD 500MB 527.6MB
Aggregate capacity available for volume use would be 2.20GB.
CLU01::> aggr add-disk -aggr
"TESTSSD3" -disklist NET-1.4 -raidgroup rg0
Info: Disks would be added to aggregate
"TESTSSD3" on node "CLU01-01" in the following manner:
First Plex
RAID Group rg0, 8 disks (block checksum, raid_dp)
Usable Physical
Position Disk Type Size Size
---------- ------------------------- ---------- -------- --------
data NET-1.4 SSD 86.56MB 113.4MB
Aggregate capacity available for volume use would be increased by 77.93MB.
CLU01::> aggr show
Aggregate Size Available Used% State RAID Status
--------- -------- --------- -----
------- ------------
TESTSSD3 2.27GB 2.27GB 0% online
raid_dp,normal
TEST 5: What happens when we try to replace the 113.4MB
SSD with a 527.6MB SSD?
CLU01::> disk replace -disk NET-1.4
-replacement NET-1.51 -action start
Warning: Replacement 520.5MB disk will be downsized
to 107.1MB. Continue? {y|n}: n
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