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Old 04-29-2016, 11:01 AM   #16
frostschutz
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Did you run `echo 3 > /proc/sys/vm/drop_caches` before each dd? Otherwise you're testing filesystem cache and not the raid itself.
 
Old 04-29-2016, 03:33 PM   #17
Elaidon
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You are right. These are the results hdd vs ramdisk raid vs tmpfs:

[root@servertest ~]# echo 3 > /proc/sys/vm/drop_caches
[root@servertest ~]# dd if=/tmp/test.img of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 0.421876 s, 2.5 GB/s
[root@servertest ~]# echo 3 > /proc/sys/vm/drop_caches
[root@servertest ~]# dd if=/ramdisk/tempfile/test.img of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 0.416269 s, 2.6 GB/s
[root@servertest ~]# echo 3 > /proc/sys/vm/drop_caches
[root@servertest ~]# dd if=/mnt/ramdisk_tmpfs/test.img of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 0.147525 s, 7.3 GB/s


according to these results, it seems much better to use tmpfs and some synchro mechanism data in tmpfs with data on hdd.

but now why the HDD read speed it is on par with that of the raid with the ramdisk? I used the write-mostly options creating the ramdisk.
Reading from the raid ramdisk should be similar to tmpfs...why not?

Last edited by Elaidon; 04-29-2016 at 03:37 PM.
 
  


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