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Re: Seeking advice on Loop-AES performance with RAID5/RAID6
George Koss wrote:
> But it all went to hell when I tried the full stack on the six drive RAID5
> or RAID6 array. Performance for writing fell to a pitiful 15 Mbytes/sec.
> I theorized that maybe the RAID helper thread was thrashing the caches, so I
> reduced the raid array chunksize to 16K, then 8K, then 4K. This didn't help
> at all. I increased the drive readahead to 1024 sectors, which seemed to
> help the read performance, but did nothing for write performance. The SATA2
> drives are already using 16 sector transfers, which appears to be the
> maximum possible. I've tried ext3, xfs, jfs and reiser3.6 filesystems,
> nothing seems to help. The best write speed I've gotten so far is 17
> Mbyte/s with RAID6 and 64K chunksizes on a reiser3.6 filesystem.
>
> RAID5 performance is terrible when I stack loop-AES on top of it. Without
> loop-AES, I'm getting 99 Mbytes/sec Read, and 105 Mbytes Write with RAID5.
> This is the performance level I want to hit, since it's just about right
> when transferring data with Gigabit ethernet.
Part of the reason why loop-AES on top of linux software RAID5 performs
badly is because loop-AES bangs the backing device with page size requests.
Linux software RAID5 wants bigger requests to be able to provide better
MBytes/s values. Partial stripe size writes are performance killers for
linux software RAID5 which has to do 2 reads and 2 writes for each write
request. I haven't looked at RAID6 parity algorithm, but I assume that it
has to read all unmodified data blocks in stripe and 3 writes for each write
request.
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Jari Ruusu 1024R/3A220F51 5B 4B F9 BB D3 3F 52 E9 DB 1D EB E3 24 0E A9 DD
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Linux-crypto: cryptography in and on the Linux system
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