wissel.net :: DAOS and Transaction Logs

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When you want to use DAOS in Domino 8.5.x you need to activate Transaction logging. DAOS allows to store attachments on cheaper disks and eliminate duplicates (Not sure if you want DAOS, use the estimator, it will tell you). BUT DAOS requires transaction logging. Transaction logging requires, to be performant, its own disk. The best practices guide states it very clearly: "It is absolutely essential to place the transaction log directory on a separate physical device devoted solely to transaction logging. Part of the performance improvement you will gain from transaction logging depends on having a separate disk, which allows fast writes to the transaction log files. Putting the transaction log on the same drive as other files — the operating system, the Domino executables, the Domino data, the OS pagefile, etc. — can result in a significant performance degradation even in comparison with an R4 server, since the server must read from and write to these files as well.".

So speak after me:"I shall use a dedicated drive for my Domino transaction log. I won't use a partition, a directory or a SAN destination. I shall use something insanely fast for this drive.".

No ifs or buts or eventuals. So the DAOS savings require some disk investment. While you are on it: make sure you use ODS51 and compression for design and data - and review the design for high performant Domino servers (Raid 10 works best). Others have recommendations too.

Comments

1 - As Sean said, basically it comes down to what works for you. I run txn logging on my laptop (8.51 client) and it only has a single disk. We have some boxes w/ 36GB of memory and put the txn logs on the same disks as the os & page file (essentially no paging). Some customers run w/ the txn logs on their SANs and don't have an issue. All of these deployments come down to it works for them, but we can't say they will work for everyone. A dedicated disk w/ its own controller will work for everyone. The best thing is to deploy the txn logs & monitor the avg write time in the stats for the txn log writes. If it goes above (I believe) 5 then you have an issue.

--Steve

Posted by Steve Watts At 13:54:38 On 01/26/2010 | - Website - |

2 - Any separate spindle is good for the TX Logs. However, a fast SSD will kill even a VelociRaptor, let alone a "normal" hard drive these days. SSDs are not cheap, but they can (and are) way faster at the high end then any other drive on the market. Some MLC SSD drives are fast, and an Intel SLC SSD leaves everything else dead in it's tracks.

{ Link }

Again, I am not saying you "need" a SSD, but also saying that they are not faster is a mis-representation of the truth.

Posted by Darren Duke At 00:41:12 On 01/26/2010 | - Website - |

3 - Would it be more appropriate to prefix your statements with "Enterprise deployments ...."

If I were advising a small shop ( say 20 people ) and they could not invest in new hardware I would seriously consider trying TLogs on the same spindle. Even before DAOS it was useful for preventing consistency checking post server crashes.

Do the foundation appliances use a separate spindle ?

I see a real danger here in being badged like MS who say you MUST have a 64 bit server. Unless it is an absolute requirement lets not say that every Domino server needs n+1 spindles ( although if you are buying a new one it would be sensible ).

I am happy to stand corrected

Sean

Posted by Sean Cull At 19:32:00 On 01/25/2010 | - Website - |

4 - @Stephan, 2nd partition is a useful idea.

@Nathan, thanks for that, it does sometimes seem that the new universal panacea is to use SSD !

Posted by Sean Cull At 23:21:32 On 01/25/2010 | - Website - |

5 - @Sean. Forgot the usual YMMV Emoticon

Nevertheless: I hardly see servers with a single disk these days. Typically OS/APPS go onto disk1 and data on disk2. Splitting disk1 into 2 partitions and use one for transaction log usually beats TL in the data directory.
But make the investment (small SATA drive for a small shop) in an extra pair of disks and watch. And now here it comes: YMMV.
Emoticon

stw
P.S.: Seems I work to long for IBM now, I usually look at enterprise deployments only.

Posted by Stephan H. Wissel At 21:16:23 On 01/25/2010 | - Website - |

6 - One thing worth noting is that if you get a dedicated spindle for your TL, there's not much reason to get an SSD. The TL pre-allocated contiguous blocks on the drive, and then writes linearly across the head, so except in the case of a crash recovery, there is no random seek on that drive. It's all sequential, and standard HDs keep up with SSDs on sequential operations.

Posted by Nathan T. Freeman At 22:47:48 On 01/25/2010 | - Website - |