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Date: Mon, 07 May 2012 10:47:26 +0000 From: Daniel Pocock <daniel@...ock.com.au> To: linux-ext4@...r.kernel.org Subject: ext4, barrier, md/RAID1 and write cache I've been having some NFS performance issues, and have been experimenting with the server filesystem (ext4) to see if that is a factor. The setup is like this: (Debian 6, kernel 2.6.39) 2x SATA drive (NCQ, 32MB cache, no hardware RAID) md RAID1 LVM ext4 a) If I use data=ordered,barrier=1 and `hdparm -W 1' on the drive, I observe write performance over NFS of 1MB/sec (unpacking a big source tarball) b) If I use data=writeback,barrier=0 and `hdparm -W 1' on the drive, I observe write performance over NFS of 10MB/sec c) If I just use the async option on NFS, I observe up to 30MB/sec I believe (b) and (c) are not considered safe against filesystem corruption, so I can't use them in practice. Can anyone suggest where I should direct my efforts to lift performance? E.g. - does SCSI work better with barriers, will buying SCSI drives just solve the problem using config (a)? - should I do away with md RAID and consider btrfs which does RAID1 within the filesystem itself? - or must I just use option (b) but make it safer with battery-backed write cache? - or is there any md or lvm issue that can be tuned or fixed by upgrading the kernel? -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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