Ever wonder what is the impact of write-through of an LSI controller in a real-world streaming server? Have no wonder anymore!
you can get several (multiple?) times slower with the write-through mode than if your controller were using the write-back mode of the cache
And it could happen any moment because when charging the battery of the LSI controller and you have set “No Write Cache if Bad BBU” the write-through would kick in. Of course, you can make a schedule for the battery charging/discharging process, but in general, it will happen and it will hurt your IO performance a lot!
In simple words a write operation is successful only if the controller confirms the write operation on all disks, no matter the data has already been in the cache.
This mode puts pressure on the disks and Write-Through is a known destroyer of hard disks! You can read a lot of administrator’s feedback on the Internet about crashed disks using write-through mode (and sometimes several simultaneously on one machine losing all your data even it would have redundancy with some of the RAID setups like RAID1, RAID5, RAID6, RAID10 and so).
srv ~ # sudo megacli -ldinfo -lall -aall
Adapter 0 -- Virtual Drive Information:
Virtual Drive: 0 (Target Id: 0)
RAID Level : Primary-1, Secondary-0, RAID Level Qualifier-0
Size : 13.781 TB
Sector Size : 512
Mirror Data : 13.781 TB
State : Optimal
Strip Size : 128 KB
Number Of Drives per span:2
Span Depth : 6
Default Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteThrough, ReadAdaptive, Direct, No Write Cache if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy : Disk's Default
Encryption Type : None
Bad Blocks Exist: No
Is VD Cached: Yes
Cache Cade Type : Read Only
Exit Code: 0x00
As you can see our default cache policy is WriteBack and “No Write Cache if Bad BBU”, the BBU is not bad, but charging! Keep on reading!
After the acquisition of LSI there was a major change with the management console utility for the MegaRAID controllers. The utility was renamed from MegaCli (MegaCli64, megacli) to
We have new controllers like AVAGO MegaRAID SAS-9361-4i and really old ones like LSI 2108 MegaRAID (in fact Supermicro AOC-USAS2LP-H8iR) and the two controllers could be manage with the new cli. even the old controller, which is on more than 8 years could be manage by the new cli.
Interesting fact is that the storcli output and argument syntax and is almost identical to the one really old cli – tw_cli – the 3Ware management utility. As you know LSI bought 3ware RAID adapter business in 2009. Keep on reading!
Here is howto article for creating a RAID5 device in MegaRAID SAS-9361-4i with SSD caching. First and really important thing is to have the CacheCade ability to the controller, which should be purchased because it is a software add-on.
To have an SSD caching your virtual raid drive (probably hard disk drives) with a MegaRAID controller one setup is the following:
Here is the screenshots’ review of LSI LSI00415 MegaRAID 9361-4i SGL controller with CacheVault Accessory kit LSI LSI00293. The controller has 3 hard disk and an SSD for the cache vault.
As you can see we use LSI, but in deed this is the AVAGO controller. First it was LSI, which was acquired by AVAGO and then AVAGO acquired Broadcom and rebranded to Broadcom. It is good to know it how these names are connected, because any controllers still use them in BIOS, management console cli, manuals and so on. You are going to see that in the controller’s BIOS and controller initialization boot up you can read only AVAGO – no LSI or Broadcom. Probably the most famous and familiar name of the three company names is LSI (hardware controller).
The screenshots are from the BIOS of “LSI LSI00415 MegaRAID 9361-4i SGL” with LSI LSI00293, CacheCade and LSI LSI00418 LSICVM02 – CacheVault Accessory kit.
So as you see you need two additional features to have a SSD as a cache device in your LSI (AVAGO/Broadcom) controller!
It happened to one of our old LSI MegaRAID 2108 controllers (AOC-USAS2LP-H8iR (smc2108) with 36 disk, 32x2T and 4x8T) to freeze and most of the processes hang up with Disk sleep. The server was up, the network was working, but no login could be successful. A hard reset was executed with the IPMI KVM. The server started up, the MegaRAID controller booted with a warning that it was shutdown unexpectedly so there could be possible loss of data and to accept it by pressing any key or “C” to boot in the WebBIOS of the controller.
To summarize it up: the LSI controller hangs up when is in the following modes:
Aborting and disabling the modes above let out controller to work till replacement. If you experience any kind of strange disk hangs or freezes you can try our solution here! Check below to see how to do it yourself.
is really old (probably 7-9 years), but still it works, so you can check if you are with the latest and greatest firmware. Hope the latest fixes more things than it beaks. To flash the firmware you need Megaraid cli and the firmware file, the two files you check in the sub-directories of https://www.supermicro.com/wftp/driver/SAS/LSI/2108/Firmware/ They are still there despite this product is discontinued. In this URL these are the latest, tested and verified versions by Supermicro so it is advisable to download them from this link or at least use the same versions if they are not available (in the future, now they are still available).
As you know LSI (they bought 3ware RAID in 2009) was bought by Avago (2013), then Avago bought Broadcom (2016 and renamed itself to Broadcom, 2018), so not so easy to find stuff for such old hardware (which still works). So this old MegaRAID controller is better managed by MegaCli despite you can do it with “storcli”, which is a modification of the tw_cli utility of 3ware RAID.