I'm trying to establish if a new disk is SMR or not, or has any other
characteristics that would make it unsuitable for use in a zfs array.
CrystalDiskMark suggests it has a speed of 6~8 MB/s in its RND4K testing.
iiuc SMR disks contain a CMR area, possibly of variable size, which is used as
a cache, so to test a drive I need to ensure I fill this cache to the drive is
forced to start shingling.
As the disk is 14TB, my first test used:
sudo fio --name TEST --eta-newline=5s --filename=/dev/sda --rw=randwrite
--size=100t --io_size=14t --ioengine=libaio --iodepth=1 --direct=1
--numjobs=1 --runtime=10h --group_reporting
which reported:
TEST: (groupid=0, jobs=1): err= 0: pid=4685: Sat Sep 5 07:42:02 2020
write: IOPS=490, BW=1962KiB/s (2009kB/s)(67.4GiB/36000002msec); 0 zone
resets
slat (usec): min=16, max=10242, avg=41.02, stdev=11.10
clat (usec): min=17, max=371540, avg=1980.75, stdev=1016.94
lat (usec): min=283, max=371587, avg=2024.00, stdev=1016.92
clat percentiles (usec):
| 1.00th=[ 486], 5.00th=[ 594], 10.00th=[ 1074], 20.00th=[ 1418],
| 30.00th=[ 1565], 40.00th=[ 1713], 50.00th=[ 1876], 60.00th=[ 2040],
| 70.00th=[ 2245], 80.00th=[ 2474], 90.00th=[ 2933], 95.00th=[ 3589],
| 99.00th=[ 4686], 99.50th=[ 5211], 99.90th=[ 8356], 99.95th=[11863],
| 99.99th=[21627]
bw ( KiB/s): min= 832, max= 7208, per=100.00%, avg=1961.66, stdev=105.29,
samples=72000
iops : min= 208, max= 1802, avg=490.40, stdev=26.31, samples=72000
I have a number of concerns about this test:
1. Why is the average speed, 2MB/s, so much lower than that reported by
CrystalDiskMark?
2. After running for 10 hours, only 67 GiB were written. This could easily
not yet have filled any CMR cache on a SMR disk, rendering the test
worthless.
I then ran some 5m tests, using different blocksizes in the command
sudo fio --name TEST --eta-newline=5s --filename=/dev/sda --rw=randwrite
--size=100t --io_size=14t --ioengine=libaio --iodepth=1 --direct=1
--numjobs=1 --runtime=5m --group_reporting --blocksize=xxx
with the result:
blksize speed(MB/s) IOPS
4k 2 490
1M 100 97
10M 130 12
100M 160 1~2
1G 160 -
3. I'm considering running a dual test, where I first write, say 10TB data
with a blocksize of 1M (28 hours), followed by 10 hours of 4k writes again.
Although the 1M block contents will be sequential data, can I assume that
enough of them will do via any CMR cache in order to fill it up and reveal any
slow down?
