Saturday, September 22, 2012

Sub-$1K Followup - Learning and Tuning

So as of a few hours ago, I've finally migrated everything off the old home SAN and onto the new one. I'll be updating that post a bit later with the promised pictures, but I must say, I am neither a photographer nor a superior case wiring guy.

Zpool status and zfs list (minus all the VM LUN's/shares)


So just so we are all on the same page, this is a home SAN used by a handful of desktops, laptops, and servers (some of which are running a few VM's). Overall performance requirements are not onerous, and certainly nowhere near an enterprise. That said, the little guy can run.

Various iozone and bonnie benchmarks run locally lead me to the belief the 2-mirror vdev 4-disk pool 'home-0' is capable of some 500 MB/s sequential large-block throughput performance best-case, and has a random 8K write IOPS potential of around 250, and a random 8K read IOPS potential of around 500. Which is in keeping with what one may expect from a pool of this configuration. The throughput is more than sufficient to overload the single Gbit NIC port, and in fact could overload a few more were I inclined to throw in a card. I'll paste one iozone output - this was write/rewrite & read/re-read on 1 GB file x 4 threads @ 128K with O_DIRECT on (even still, reads are through ARC, clearly).

        File size set to 1048576 KB
        Record Size 128 KB
        O_DIRECT feature enabled
        Command line used: iozone -i 0 -i 1 -t 4 -s 1G -r 128k -I
        Output is in Kbytes/sec
        Time Resolution = 0.000001 seconds.
        Processor cache size set to 1024 Kbytes.
        Processor cache line size set to 32 bytes.
        File stride size set to 17 * record size.
        Throughput test with 4 processes
        Each process writes a 1048576 Kbyte file in 128 Kbyte records

        Children see throughput for  4 initial writers  = 4013508.50 KB/sec
        Parent sees throughput for  4 initial writers   =  133536.91 KB/sec
        Min throughput per process                      =  942170.62 KB/sec
        Max throughput per process                      = 1084839.00 KB/sec
        Avg throughput per process                      = 1003377.12 KB/sec
        Min xfer                                        =  910720.00 KB

        Children see throughput for  4 rewriters        = 4426626.19 KB/sec
        Parent sees throughput for  4 rewriters         =  187908.93 KB/sec
        Min throughput per process                      = 1016124.94 KB/sec
        Max throughput per process                      = 1168724.50 KB/sec
        Avg throughput per process                      = 1106656.55 KB/sec
        Min xfer                                        =  913792.00 KB

        Children see throughput for  4 readers          = 9211610.25 KB/sec
        Parent sees throughput for  4 readers           = 9182744.11 KB/sec
        Min throughput per process                      = 2298095.25 KB/sec
        Max throughput per process                      = 2309781.00 KB/sec
        Avg throughput per process                      = 2302902.56 KB/sec
        Min xfer                                        = 1043328.00 KB

        Children see throughput for 4 re-readers        = 11549440.75 KB/sec
        Parent sees throughput for 4 re-readers         = 11489037.68 KB/sec
        Min throughput per process                      = 2084150.50 KB/sec
        Max throughput per process                      = 3724946.00 KB/sec
        Avg throughput per process                      = 2887360.19 KB/sec
        Min xfer                                        =  590848.00 KB

To achieve this, I have the following minimal tunables for ZFS in my loader.conf:

### ZFS
# still debating best settings here - very dependent on type of disk used
# in ZFS, also scary when you don't have homogeneous disks in a pool - 
# fortunately I do at home. What you put here, like on Solaris,
# will have an impact on throughput vs latency - lower = better latency, 
# higher = more throughput but worse latency - 4/8 seem like a decent 
# middle ground for 7200 RPM devices with NCQ

# 5/1 is too low, and 30/5 is too high - best wisdom at the moment for a 
# good default is 10/5

# it is the rare workload that benefits from this more than it hurts


What's more important is how it performs to clients. My main box is (gasp) a Windows 7 desktop.. I ran around a bit and found 'ATTO', which I recall a customer once using to benchmark disks on Windows. I can't speak to its 'goodness', but it returned results I'd expect with Direct I/O checked on or off.

I'm only really interested in the transfer sizes I ever expect to use, so 8K to 128K, and I maxxed out the 'length' ATTO could go to, 2 GB, which I might add is still well within the range of my ARC, but Direct I/O checkbox in ATTO works quite well and seems to force real reads. As you can see in the first picture, the iSCSI disk (F:) performs quite admirably considering this is between two standard Realtek NIC's on desktop motherboards going through a sub-$200 home 1 Gbit switch, all running at standard 1500 MTU.

8 KB to 128 KB - 2 GB file - Direct I/O - 4 queue
For giggles, in the next picture you'll see the same test performed with the Direct I/O checkbox removed. Look at me go! 4.1 GB/s read performance - across a 1 Gbit link! Obviously a little broken. ATTO seemed to give up on the 128 K (I did a test for the full xfer sizes up to 8 M, and it completely crapped out on the 8M xfer size one, too, reporting nothing for read performance).

8 KB to 128 KB - 2 GB file - no Direct I/O - 4 queue
For iSCSI, I opted for the istgt daemon, not the older offering. My istgt.conf file is below in its uncommented entirety. Note that my NodeBase and TargetName are being set the way they are to mimic the settings from the old SAN, thereby removing my need to touch the iSCSI setup on my machines. I've left out most the LUN's, but left two to show how they are defined in this file:

  Comment "Global section"
  NodeBase ""
  PidFile /var/run/
  AuthFile /usr/local/etc/istgt/auth.conf
  LogFacility "local7"
  Timeout 30
  NopInInterval 20
  DiscoveryAuthMethod Auto
  MaxSessions 32
  MaxConnections 8
  MaxR2T 32
  MaxOutstandingR2T 16
  DefaultTime2Wait 2
  DefaultTime2Retain 60
  FirstBurstLength 262144
  MaxBurstLength 1048576
  MaxRecvDataSegmentLength 262144
  InitialR2T Yes
  ImmediateData Yes
  DataPDUInOrder Yes
  DataSequenceInOrder Yes
  ErrorRecoveryLevel 0
  Comment "Internal Logical Unit Controller"
  AuthMethod CHAP Mutual
  AuthGroup AuthGroup10000
  Portal UC1
  Comment "T1 portal"
  Portal DA1
  Comment "Initiator Group1"
  InitiatorName "ALL"
  Mapping PortalGroup1 InitiatorGroup1
  AuthMethod Auto
  AuthGroup AuthGroup1
  UnitType Disk
  LUN0 Storage /dev/zvol/home-0/ag_disk1 Auto
  LUN1 Storage /dev/zvol/home-0/steam_games Auto

CIFS / Samba

What about CIFS? Yes, I make some use of it (sigh). What can I say, I'm lazy. I'm not sure how to 'benchmark' CIFS, apparently it's not something often done. I found a 1+ GB .iso file and copied it to my OS SSD and then back to a new place on a share, and captured these two shots. To the left, you have me copying the ISO from Z: (a CIFS network mapped drive) to My Documents (my OS SSD). The speed range was pretty consistent, in the 80-90 MB/s area.
From CIFS Share to OS SSD

To the right you see the same, but in reverse -- copying the file from the OS SSD to a folder on the Z: network share. Again, performance in the 80-90 MB/s. It never dipped on either transfer. I tried various other files and the speed range was a bit erratic at times (as CIFS is wont to do), with the lowest I saw being 68 MB/s and the highest being 192 MB/s (hah).
From OS SSD to CIFS Share

Part of reaching this level of performance with CIFS to a FreeBSD Samba install was in the tuning, however. I went with samba version 3.6, and my smb.conf entries for ZFS/AIO can be found below. Please bear in mind I use CIFS at the home for unimportant data that is snapshotted regularly and I can afford to lose a few minutes of work - and am impatient and don't want to wait forever for a file copy on it, etc, and at the moment the home SAN has no SSD for slog. These settings are very likely not data safe for in-transit data if power is lost (mostly due to aio write behind = yes):



  socket options = IPTOS_LOWDELAY TCP_NODELAY SO_RCVBUF=131072 SO_SNDBUF=131072
  use sendfile = no
  min receivefile size = 16384
  aio read size = 16384
  aio write size = 16384
  aio write behind = yes


I also have the following related changes to my /boot/loader.conf file:



And to my /etc/rc.conf file:



In all, I'm impressed on the whole, but finding a few things lacking. One example, while it is of no consequence to me, would be as others have pointed out to me that if I had been doing FC Target stuff on my Solaris SAN, I'd have been unable to try this out - FreeBSD lacking good FC Target capability like COMSTAR has. The istgt package seems to do iSCSI great, but it is limited to iSCSI.

There were also various personal learning curves. For awhile, on boot the box would be unable to initially do istgt, and it turned out that while I had zfs_load="YES" in my /boot/loader.conf file, I did not have zfs_enable="YES" in my /etc/rc.conf file. This is sneaky, because ZFS worked just fine (I could type 'zfs list' right after boot, and there were my datasets), but even after doing a zfs list, istgt wouldn't work until I created or renamed a zvol. It turned out FreeBSD wasn't creating the /dev/zvol links that istgt was looking for until I created or renamed a zvol, whereas once I added zfs_enable="YES" to /etc/rc.conf, they were instantiated at boot time just fine.

I find the ports system both flexible, powerful, and foreign. I'm probably pulling a FreeBSD admin faux pas by installing the new 'pkg' system but both before and after installing it have randomly used 'make install' in /usr/ports when necessary (like to compile Samba 3.6 with the options I wanted).

I do enjoy learning new things, though, so I'm quite pleased with the time spent and the results so far. My next steps will be:

  • creating a robust automatic snapshot script/daemon
  • seeing if I can't dust off my old Python curses skills and build a simple one screen health monitor with various SAN-specific highlights to leave running on the LCD monitor plugged into the box
  • going downstairs right now and finding the Crown and a Coke - pictures on other post can wait



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