Performance issue with FW800 connection order?

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Performance issue with FW800 connection order?

Post by RyanAlan » Mon Sep 24, 2012 12:16 am

I'm using 3 firewire 800 drives: 2 3Tb WD drives and 1 80Gb Intel SSD (~3 years old). I placed the SSD before the 2 WD disks for "optimal" firewire performance.

When I first configured my zpool I used a SSD for a ZIL and L2ARC cache purposes. The performance was terrible so I removed the SSD and ran a simple mirror with the 2 WD drives, this configuration ran well, here is a baseline:
Image

I added the SSD back into my firewire daisy chain and realized a huge hit to performance. This is with the SSD in the first position in the FW chain:
Keep in mind that graph displays 90 seconds of read/write speed!
Image

I received a few messages in the console at that time:
Code: Select all
com.apple.kextd: Can't create kext cache under / - owner not root.  (repeated ~10 times)

this one showed up quote a bit too:
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WindowServer: CGXSetTrackingAreaEnabled : Invalid tracking area 0x############ (where ## is changing hex value)


Here is the same hardware configuration writing the same 3Gb file to the SSD:
Image

I shutdown my system and moved the SSD to the last position in the FW chain, the performance reverted back to normal:
Image

In the same HW configuration the SSD performed well too:
Image

Seems like a faulty FW port or cable running from the SSD, right? Here's the SSD running between the two WD drives:
Image

Strange, right? Seems like the SSD FW ports and cables are fine...

diskutil list output:
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/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *240.1 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            159.0 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
   4:       Microsoft Basic Data BOOTCAMP                80.2 GB    disk0s4
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *80.0 GB    disk1
   1:                        EFI                         209.7 MB   disk1s1
   2:                  Apple_HFS SSD80                   79.7 GB    disk1s2
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *3.0 TB     disk2
   1:                        EFI                         209.7 MB   disk2s1
   2:                        ZFS                         3.0 TB     disk2s2
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *3.0 TB     disk3
   1:                        EFI                         209.7 MB   disk3s1
   2:                        ZFS                         3.0 TB     disk3s2
/dev/disk4
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:             zfs_pool_proxy zData                  *3.0 TB     disk4


zfs list output:
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NAME     USED   AVAIL   REFER  MOUNTPOINT
zData   133Gi  2.56Ti   133Gi  /Volumes/zData


system:
iMac 27-inch, Late 2009
OS 10.8.2 build 12C54
12Gb RAM

Any ideas?
RyanAlan Offline


 
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order of things on the bus, and combinations on a single SSD

Post by grahamperrin » Tue Sep 25, 2012 1:31 am

RyanAlan wrote:… Any ideas?


None about the effect of order on the FireWire bus (sorry) but I'll be very interested in an eventual expiation from someone else.

I never used a dedicated device for L2ARC or ZIL, but I do have two LaCie hard disk drives (sometimes a third, with a 400 connection) on the FireWire 800 bus of my MacBookPro5,2. (Off-topic: the first JHFS+ slice of the internal hybrid drive is dedicated to swap.)

Your configuration got me wondering about something other than order: For L2ARC and ZIL: is it better to have one large SSD for both, or two smaller SSDs?

Postscript

Ryan, please: are the performance issues apparent only in utilities such as iStat Menus?

Or – more importantly – are performance issues equally tangible in your hands-on use of the computer?

(Whilst the graphs in the opening post are are clear, it's known that iStat Menus can't properly represent logical volumes in CoreStorage world, and so on. So I wonder about its ability to measure novel arrangements where one device in a chain is effectively a multipurpose cache for other devices.)

For reference: a graph of warmup, over thirty hours, at L2ARC Screenshots (Brendan Gregg).
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Re: Performance issue with FW800 connection order?

Post by RyanAlan » Thu Sep 27, 2012 1:13 am

The performance difference is quite tangible! 3Gb takes about 1 minute with the "fast" configuration (HDD-HDD-SSD) and 1 hour+ on the "optimal" configuration (SSD-HDD-HDD).

I am aware using a single SSD for the ZIL and L2ARC is not an ideal solution. It might be worth mentioning, I am not running a highly active server, this is just for iTunes and iPhoto libraries being accessed by 2 machines! The idea is to test the setup and see what performance improvements the SSD will net.
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Re: Performance issue with FW800 connection order?

Post by grahamperrin » Fri Oct 18, 2013 9:53 pm

Is the SSD multi-level cell (MLC) or single-level cell (SLC)? In Stack Exchange, the question gained what seems (to me) a good answer.

For test purposes: if you give the SSD to either ZIL or L2ARC (not both), then put it again in first place on the FireWire bus, does the performance of the system suffer again in the same way?
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