I'm trying to migrate my mariadb data directory with several tables with page compression from 10k to 15k disks (both ext4 filesystem). I've tried stopping the mariadb process, then do a regular cp, but it's very slow. The data directory is just 100GB large, it starts very well, comes to 60GB, then it's become very slow, copying just a few hunder KB per second, taking forever to complete. I also tried using mariabackup to copy from one disk to another, but it came to 78GB, 4 cores running on 100% (mariabackup --parallel=4) but very slow progress.

Found this: https://www.percona.com/blog/2017/11/20/innodb-page-compression/

Is there anything that can be done to have some reasonable speeds?

The tables are partitioned page compressed tables like:
CREATE TABLE `cqrs_event` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`event_id` char(36) COLLATE utf8_unicode_ci NOT NULL,
`event_date` datetime NOT NULL,
`event_date_u` int(10) unsigned NOT NULL,
`aggregate_type` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
`aggregate_id` varchar(64) CHARACTER SET utf8 DEFAULT NULL,
`sequence_number` int(10) unsigned DEFAULT NULL,
`payload_type` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`payload` longtext COLLATE utf8_unicode_ci NOT NULL,
`metadata` longtext COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`,`event_date`),
KEY `ix_cqrs_event_aggregate` (`aggregate_type`,`aggregate_id`,`sequence_number`),
KEY `ix_cqrs_event_dates` (`event_date`,`event_date_u`),
KEY `ix_cqrs_event_id` (`event_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci `PAGE_COMPRESSED`=1
PARTITION BY RANGE (to_days(`event_date`))
(PARTITION `to_20190127` VALUES LESS THAN (737451) ENGINE = InnoDB,
PARTITION `to_20190203` VALUES LESS THAN (737458) ENGINE = InnoDB,
PARTITION `to_20190210` VALUES LESS THAN (737465) ENGINE = InnoDB,
...

Thanks