any one has same mystical issue ?
On PERC H730 Mini (Embedded) with latest FW: 25.5.2.0001 I have RAID: 0 with 4x SSD.
PERC H730 Mini (Embedded) with latest FW: 25.5.2.0001 in Write Cache: Write through works much faster then Write-Back/Forced Write-Back and read works much faster with No Read Ahead
Write: Write Back
write: io=4096.0MB, bw=376306KB/s, iops=94076, runt= 11146msec
write: io=4096.0MB, bw=174828KB/s, iops=43707, runt= 23991msec
Write: Write Through
write: io=4096.0MB, bw=451875KB/s, iops=112968, runt= 9282msec
write: io=4096.0MB, bw=464691KB/s, iops=116172, runt= 9026msec
Read: Read Ahead
read : io=4096.0MB, bw=483048KB/s, iops=120761, runt= 8683msec
read : io=4096.0MB, bw=492694KB/s, iops=123173, runt= 8513msec
Read: No Read Ahead
read : io=4096.0MB, bw=570887KB/s, iops=142721, runt= 7347msec
read : io=4096.0MB, bw=530455KB/s, iops=132613, runt= 7907msec
How its possible?
test been made using:
"fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test --filename=test --***=4k --iodepth=64 --size=4G --readwrite=randwrite"
In most instance WB is faster then WT but.....
Most data requests on servers, and raid adapters are set up for small data chunks' for the most part, general server use, WB will be faster as some or all the data is retrieved from the raids cache.. Raid adapter cache once filled with data actually adds overhead unless data is retrieved from the cache. With a large amount of data such as 4Gig, very little data will be retrieved from the cache as the file is multiple times the size of raid cache memory.
Other variables.... test programs ability to deal with the raid, drive parameters.