aero.108
1 Copper

Write through / No read ahead works much faster then Write Back (Forced write back) on PERC H730 Mini (Embedded) with latest FW: 25.5.2.0001

Hi guys,

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
Sequential write:
write: io=4096.0MB, bw=376306KB/s, iops=94076, runt= 11146msec
Random write:
write: io=4096.0MB, bw=174828KB/s, iops=43707, runt= 23991msec

Write: Write Through
Sequential write:
write: io=4096.0MB, bw=451875KB/s, iops=112968, runt=  9282msec
Random write:
write: io=4096.0MB, bw=464691KB/s, iops=116172, runt=  9026msec

Read: Read Ahead
Sequential read:
read : io=4096.0MB, bw=483048KB/s, iops=120761, runt=  8683msec
Random read:
read : io=4096.0MB, bw=492694KB/s, iops=123173, runt=  8513msec

Read: No Read Ahead
Sequential read:
read : io=4096.0MB, bw=570887KB/s, iops=142721, runt=  7347msec
Random read:
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"

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1 Reply
pcmeiners
4 Tellurium

RE: Write through / No read ahead works much faster then Write Back (Forced write back) on PERC H730 Mini (Embedded) with latest FW: 25.5.2.0001

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.

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