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Write speeds


maciekish

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Hi,

I have 3x Seagate IronWolf 10Tb drives with one as parity and a 1Tb SSD as cache. Once the cache is full and the IronWolf internal 256Mb cache is full write speeds drop to 40Mb/s from 115Mb/s. I realize unRAID has to read for each write but shoud it really be this slow or am i doing it wrong?  LSI 9201-16i controller, same speeds on mainboard controller as well.

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6 hours ago, maciekish said:

Hi,

I have 3x Seagate IronWolf 10Tb drives with one as parity and a 1Tb SSD as cache. Once the cache is full and the IronWolf internal 256Mb cache is full write speeds drop to 40Mb/s from 115Mb/s. I realize unRAID has to read for each write but shoud it really be this slow or am i doing it wrong?  LSI 9201-16i controller, same speeds on mainboard controller as well.

Each ‘write’ involves read of both of the data drive and parity drive, and then writes to both drives (totalling 4 I/O operations) with a drive revolution required between the reads and writes.   As was mentioned this typically drops the throughput to around 40 MB/sec.     Turbo mode can speed this up by only doing a single I/O operation to the parity and target data drive at the expense of doing reads from all other drives (which can be done in parallel).   This can reduce delays caused by disk latency at the cost of needing all drives spinning.

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