2008/1/23, Martin Knoblauch <[EMAIL PROTECTED]>: > Please CC me on replies, as I am not subscribed. > > Hi, > > for a while now I am having problems writing large files sequentially to > EXT2 filesystems on CCISS based boxes. The problem is that writing multiple > files in parallel is extremely slow compared to a single file in non-DIO > mode. When using DIO, the scaling is almost "perfect". The problem manifests > itself in RHEL4 kernels (2.6.9-X) and any mainline kernel up to 2.6.24-rc8. > > The systems in question are HP/DL380G4 with 2 cpus, 8 GB memory, > SmartArray6i (CCISS) with BBWC and [EMAIL PROTECTED] disks in RAID5 > configuration. Environment is 64-bit RHEL4.3.
I've seen similar problems on HP DL380 G4 (SmartArray 6i) and HP DL385 G5 (SmartArray P400). RHEL 4, kernel 2.6.9 and reiserfs had siginifcantly worse I/O performance than a Gentoo box running 2.6.18 (iirc) when I did some I/O-test with different distributions on a HP DL380 G4 before deploying the machine in production. Switching I/O-schedulers on RHEL4 didn't help either. Also, I'm having awful I/O-performance with a DL385 G2/2x2.6GH/4GB running MySQL 5 on Ubuntu 7.10 (kernel 2.6.22). It previously ran Ubuntu 7.04 (kernel 2.6.20) which had the same issue. On this server MySQL stalls for a long time waiting for I/O after SQL updates that causes lots of writes. I've been trying to mitigate the problems by adding 512MB Batterybacked Writecache and lately also switching from RAID1 to RAID 1+0 (4x72GB 15k SAS disks). It's better but there are still issues. I think after switching to RAID 1+0 I'm now getting around 50-70 MB/s, which is 1.5-2.0 times the performance I had before. Running sync on any of the servers while there are dirty pages to be written (according to /proc/meminfo) virtually kills all I/O until the sync completes. I don't have much experience with other RAID controllers than the SmartArray and naturally don't know what to expect, but I sure think it should be better. I'm getting much better performance out of an ordinary "home computer" that has 4 standard disks in RAID 1+0 configuration (software; Linux md) and AES encryption with dm-crypt. Below are some numbers. HP DL385 G5, 2x2.6GHz/2GB/4x72GB in RAID1+0, kernel 2.6.22 (Ubuntu 7.10 x64) ==== # sync; time sh -c "dd if=/dev/zero of=/data/test bs=1024k count=8192;sync" dd: writing `/data/test': No space left on device 6187+0 records in 6186+0 records out 6487523328 bytes (6.5 GB) copied, 113.756 seconds, 57.0 MB/s real 1m56.916s user 0m0.050s sys 0m31.040s HP DL385 G5, 2x2.6GHz/4GB/4x72GB in RAID1+0 512MB BBWC, kernel 2.6.22 (Ubuntu 7.10 x64) === # sync; time sh -c "dd if=/dev/zero of=/data/test bs=1024k count=8192;sync" 8192+0 records in 8192+0 records out 8589934592 bytes (8.6 GB) copied, 120.797 seconds, 71.1 MB/s real 2m1.883s user 0m0.020s sys 0m26.530s -- noah -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
