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I recently bought a 120 GB OCZ Vertex 3 and stuck in my 2009 Macbook White, together with a optibay-adapter for the old 500 GB HDD and configured them as a corestorage "fusion drive" by using the Jolly Jinx recipe.

It seems to work as expected, that is, as one big volume and I even think I have seen the system move data between disk 0 and disk 1 after accessing some files heavily.

However, as I am copying a 50 GB VMWare disk image from a usb HDD, the write performance is quite poor due to a ginormous amount of "stuttering".

I have tried running iostat -w1 and it shows me that a) almost all data is written to the HDD as expected, and b) the disk activity shifts between 2-8 seconds of writing 15-50 MB/s to the HDD followed by 25-40 seconds of no drive activity at all neither on the SSD or the HDD.

Output from iostat -w (disk0 = SSD, disk1 = HDD, disk3 = USB-HDD).

        disk0           disk1           disk3       cpu     load average
KB/t tps  MB/s     KB/t tps  MB/s     KB/t tps  MB/s  us sy id   1m   5m   15m
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   4  5 90  0.62 0.71 0.93
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   4  2 94  0.62 0.71 0.93
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   4  5 91  0.62 0.71 0.93
4.17   3  0.01     0.00   0  0.00     4.00   1  0.00   3  2 94  0.62 0.71 0.93
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   4  4 92  0.62 0.71 0.93
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   3  2 96  0.57 0.70 0.92
19.61 131  2.50   844.32  37 30.45   128.00  99 12.35  12 12 76  0.57 0.70 0.92
14.56 100  1.42   914.73  41 36.55   128.00 306 38.30   6  8 86  0.57 0.70 0.92
20.40 120  2.39   916.84  43 38.42   128.00 304 38.04  22 16 62  0.57 0.70 0.92
12.20 141  1.68   856.36  45 37.59   128.00 305 38.08  24 14 63  0.57 0.70 0.92
24.24  99  2.34   896.00  43 37.55   128.00 305 38.18   9 11 80  0.53 0.69 0.92
21.40 120  2.50   906.89  47 41.55   128.00 307 38.43   4  8 88  0.53 0.69 0.92
12.14 145  1.72   868.67  42 35.56   128.00 306 38.31   6 11 83  0.53 0.69 0.92
21.51 119  2.50   906.89  47 41.58   128.00 307 38.33  12 10 78  0.53 0.69 0.92
13.71  63  0.84   856.00  16 13.35   128.00 188 23.45   6  9 85  0.53 0.69 0.92
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00  16  5 79  0.56 0.69 0.92
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00  36 12 52  0.56 0.69 0.92
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   9  4 87  0.56 0.69 0.92
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   9  6 85  0.56 0.69 0.92
0.00   0  0.00     0.00   0  0.00     0.00   0  0.00   7  3 90  0.56 0.69 0.92

The system doesn't seem overloaded cpu-wise and there are no other programs doing IO heavy stuff. The 510 GB volume is around 45% full and the system is freshly installed a week ago. Both drives are running at SATA2 speed of 3 Gbps acc. to system information.

I'd expect it to write a steady 40-50 MB/s to the HDD, once it has filled up the write buffer on the SSD.

Is this normal Fusion Drive behavior and if not, how do I troubleshoot it?

Update: After some days of no response here nor at ocztechnologyforums, I decided to backup and reinstall the system on the SSD without the fusion drive and with the HDD mounted as /Volumes/Data. This revealed that there is a problem writing to the HDD while reading or writing to/from the SSD. Reading from HDD while writing to SSD works fine. So the problem appears unrelated to fusion drive.

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closed as too localized by Daniel Lawson Jun 19 '13 at 13:37

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