A lot have been written about Battery Learning Cycle problems and its impact to MySQL Performance. Here are couple of links (1,2). It is good to see though there are some controllers coming out which solve this problem, namely Adaptec 5Z series controllers (Z stands for Zero Maintenance). This is not quite new technology they have appeared on market about 2 years ago but it is just now we can state they have been working well for number of customers.
As Explained in this PDF ZMCP (Zero-Maintenance Cache Protection) does not use battery but instead Capacitor plus flash. Capacitor provides enough energy for contents of DRAM to be flushed to supplied Flash module. This solution helps not only with battery discharge/learn cycle many Battery Backup Unit (BBU) based controllers help but also gives you a lot longer time to recover the data as it does not depend on battery any more.
The models which are known to work are Adaptec 5405Z, Adaptec 5445Z and Adaptec 5805Z which have their main difference in amount of internal and external hard drive connections they provide.
Some Newer Adaptec Controllers also offer using SSD as a cache with technology called MaxIQ. Namely Adaptec 5805ZQ might be of interest as it combines both ZMCP and MaxIQ technologies. I have not seen much use of this kind of cache with MySQL in practice though. If you’re using it please share your experiences. if you’re looking for more information this PDF might be good place to start.
For the reference here is how configuration output information looks for such controllers:
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[root@sl2 ~]# /usr/StorMan/arcconf getconfig 1 AD Controllers found: 1 ---------------------------------------------------------------------- Controller information ---------------------------------------------------------------------- Controller Status : Optimal Channel description : SAS/SATA Controller Model : Adaptec 5405Z Controller Serial Number : 1B1811A16A3 Physical Slot : 1 Temperature : 76 C/ 168 F (Normal) Installed memory : 512 MB Copyback : Disabled Background consistency check : Disabled Automatic Failover : Enabled Global task priority : High Performance Mode : Default/Dynamic Stayawake period : Disabled Spinup limit internal drives : 0 Spinup limit external drives : 0 Defunct disk drive count : 0 Logical devices/Failed/Degraded : 1/0/0 SSDs assigned to MaxIQ Cache pool : 0 Maximum SSDs allowed in MaxIQ Cache pool : 8 MaxIQ Read Cache Pool Size : 0.000 GB MaxIQ cache fetch rate : 0 MaxIQ Cache Read, Write Balance Factor : 3,1 NCQ status : Enabled Statistics data collection mode : Enabled -------------------------------------------------------- Controller Version Information -------------------------------------------------------- BIOS : 5.2-0 (18252) Firmware : 5.2-0 (18252) Driver : 1.1-5 (24702) Boot Flash : 5.2-0 (18252) -------------------------------------------------------- Controller ZMM Information -------------------------------------------------------- Status : ZMM Optimal |
As you can see there is no information about BBU here instead it is replaced with status of ZMM (Zero Maintenance Module). It also reports information about MaxIQ which is confusing as MaxIQ is not supported by this controller per technical specs.
If you would like to check the cache status it should be in the logical drive information:
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[root@sl2 ~]# /usr/StorMan/arcconf getconfig 1 LD Controllers found: 1 ---------------------------------------------------------------------- Logical device information ---------------------------------------------------------------------- Logical device number 0 Logical device name : RAID10-A RAID level : 10 Status of logical device : Optimal Size : 571382 MB Stripe-unit size : 256 KB Read-cache mode : Enabled MaxIQ preferred cache setting : Disabled MaxIQ cache setting : Disabled Write-cache mode : Enabled (write-back) Write-cache setting : Enabled (write-back) when protected by battery/ZMM Partitioned : Yes Protected by Hot-Spare : No Bootable : Yes Failed stripes : No Power settings : Disabled -------------------------------------------------------- Logical device segment information -------------------------------------------------------- Group 0, Segment 0 : Present (0,1) WD-WXL1E11WFZ23 Group 0, Segment 1 : Present (0,0) WD-WX11DB003670 Group 1, Segment 0 : Present (0,2) WD-WX11DB006532 Group 1, Segment 1 : Present (0,3) WD-WX11DB006553 |
This tells us there is one RAID10 module which is currently operating in Write-Back cache mode now (Write-Cache mode line) and it is set into “Enabled (write-back) when protected by battery/ZMM”, which is setting you want to have as you want to ensure it goes to write through mode if ZMM fails.
If you have any experience with these controllers or other controllers using similar technology please feel free to share.
